Hi Nicole,
Thank you for the question.
It seems to be the same issue as this topic:
As Inkdrop uses : for its document IDs, it also uses the character in the backup filenames.
So, it assumes that you have a set of backup files with correct filenames, not being url-encoded like %3a.
I was testing it with Dropbox and Google Drive and found that they worked fine with those filenames.
But it turns out recently that other cloud storage services don’t deal with special characters very well, unfortunately.
So, the answer is yes. Please use Dropbox or Google Drive to sync your backup for now.
I’ll continue the discussion on the above topic.