I have had the same issues as all of you but with a different phone. My phone is a Motorola 2nd Gen with 4G lite.
I contacted their online support and thought I'd include the entire chat here for all of you to read. Hope it sheds some light on this for some of you. I'm heading out to buy a new sd card soon.
-START OF SUPPORT CHAT WITH MOTOROLA-
Karen: Hello! Welcome to Motorola Canada technical Support! How are you doing today? My name is Karen. How may I help you?
Me: Like many Motorola owners... my phone has decided to no longer function with, or read, my SD card.
Me: This is a recent issue that surfaced after the Marshmallow update.
Karen: I am really sorry to read about the inconvenience you are having but I will be happy to assist you today.
Me: I have been reading online about this issue with many other marshmallow users and some of them have purchased up to 4 different (and new) sd cards that all eventually fail... rendering them useless.
Karen: Could you please provide me the IMEI number of your phone?
It can be found on the side of the box, under Settings > About Phone > Status, or by dialing *#06# on the main screen of your handset
Me: Ok... hold on...
Me: Number Provided to Tech Support
Karen: Thanks.
Karen: Let me ask you, have you tried any troubleshooting step on the device?
Me: Just tried reinstalling the card, tried reformatting it, tried using it as both internal and external storage, but it won't format and states this card is not supported. Also tried it on my computer but it can no longer be read by it (or anything for that matter).
Karen: I see, I am sorry for the inconvenience.
Karen: Do you have this problem only with this card or with all?
Me: I put it in my wife’s phone as well... we have the EXACT phones... however she has NOT upgraded to the new operating systems... and when I put the card in her phone it used to recognized it... but now it does not.
Karen: I see, may I know what type of card are you using?
Me: SONY...Micro SD... 32 GB... 700 MB/S… HC
Karen: Do you see any number on the card?
Me: wow... yeah hard to read... hold on...
Me: 90973539
Karen: I mean something similar to this https://motorola-global-portal.custhelp.com/euf/assets/images/faqs/Marshmallow/sd-card/sd-1.PNG
Me: it also says... SR-32UY2
Karen: I would like you to verify that because for this Android version. We recommend use of a high speed card , such as a UHS-1 type.
Me: Nothing on this card refers to UHS-1
Me: not that I can see
Karen: Then this could be the reason why it does not work properly on the device.
Me: it worked fine until the latest operating system update... so how long has UHS-1 been a preferred SD card type?
Me: Remember... other people have tried up to 4 different cards that all eventually fail...
Me: So are you recommending that I purchase a UHS-1 type sd card?
Karen: All devices are different depending on the usage, we may have to check if those have tried high speed cards.
Karen: I would recommend you to format the card from a computer, but if the issue persists, the best will be to upgrade your SD card.
Me: The card will NOT format on my computer... It no longer shows up when I try to view it with my computer
Karen: Oh I am really sorry, then in that case you can try to format it from the other phone and then on the PC.
Karen: I would suggest you to try as well another card on the phone before purchasing a new one.
Me: Has Motorola recommended using a UHS-1 SD card with this phone from day 1... or do they CHANGE their recommendations of SD card types based on each new operating system?
Me: I don't have any other sd cards... do people just have them laying around the house normally...?
Karen: Some requirements are changing depending on the latest versions, since systems are beings upgrading everyday the same happens to the SD cards since lower cards could not work properly.
Me: So would a higher-speed card ALWAYS work as expected even after major operating system changes or updates?
Karen: Correct, cards has to be up to date as well.
Me: Okay hold on a minute here... you need to clarify exactly what you're telling me. Are you saying that it's possible that each time Motorola updates or changes the operating system for this phone that I may have to purchase a new SD Card to ensure it works?
Karen: Not exactly, it could pass many years.
Me: I see... but there is still that risk at sometime that the card may need to be updated.
Me: I have had my phone less than 1 year and already my sd card is no longer compatible with my phone... as a matter of fact the phone has now destroyed the card... nothing can access it or read it anymore...
Karen: This cannot guarantee but as mentioned it could pass many years.
Me: Here's what worries me... other people have tired a lot of different cards and eventually they all fail... this obviously costs money that no one can get back. Are you aware of any issues with these phones that can cause the SD Cards to become unusable...?
Me: I'm willing to purchase a UHS-1 SD Card but if it eventually fails I'm gonna be real unhappy. However before I jump to conclusions I will have to try that first.
Karen: But as I was telling you, every phone is different and we do not know what type of cards they have used.
Me: Ok true... fair enough...
Karen: I understand you, in this is why I recommend you to try to get first another card, any other and check if that work on the phone.
Me: I will try the UHS 1 SD Card
Me: Does you have an exact recommendation? Sony? Sandisk?
Me: In other words... are there any SD Cards that Motorola recommends for use in their devices?
Karen: We cannot recommend any brand in specific but as far as it is a higher speed car it will be okay.
Karen: You can find more details about using SD card on Marshmallow: https://motorola-global-portal.custhelp.com/app/answers/prod_answer_detail/a_id/109134/p/1449,9582
Me: Ok so... if I purchase a UHS 1 SD Card will it automatically be fast enough?
Karen: Correct but if you have the chance to try another SD card before purchasing it, it will be better.
Me: I have no idea how to try another SD Card before purchasing it. My current card transfers data at 70 MB/s.... what does Motorola recommend?
Me: Does Motorola recommend a minimum MB/s for these phones?
Me: That might help me in my search
Karen: This could depend on the card that's why the only we recommend to check is if the card is high speed.
Me: Okay... well thank you for your time. Hopefully a newer faster card will work.
Karen: You're welcome!
Me: Have a great day!
Karen: Thanks!
Karen: I wonder if besides that you have any other question or something else that I can do for you?
Me: Nope... that's it....
Karen: Alright!
Karen: Thank you for contacting Motorola chat support. Have a Wonderful day!
Karen: Bye!