Hi
Have the same phone and encountered the same issue. My SD card is only 32GB but I'm not a heavy app user anyway. Not sure if FB was the cause but removed all apps anyway. In settings- storage I changed preferred install location to SD card and changed default write disk to SD card. I re-started, then re-installed each app. I noticed that although it still installed the apps to internal storage, it now allowed me to move the app to the SD card which I could not do before. Please note though that some apps will only work from internal storage, like my weather app which I have since removed...but for a different reason. FB is still in the dog house however, but thats just me going cold turkey on social media this month.
Hope this helps
Good Luck
SNikki