I haven’t figured out the root cause for this issue yet but seem to have a work around that worked for me. Turn on airplane mode. Ensure Wi-Fi is also off.
open my ministry, click on backup. It will open the overlay with an error. There you can unlink Dropbox.
force close My Ministry.
once you unlink Dropbox, turn airplane mode off and Wi-Fi on again
start My Ministry and the relink to your Dropbox account.
that seemed to fix it for me for now.