I also ran into the same exact problem today. I installed Backblaze this morning and tried to adopt a previous backup and got the same error. I just restarted as a new backup and moved on.
But now reading what renaudg mentioned I took a look at the log files and I see the same error:
20191008161659 - ERROR could not read attribute named supports_inherit
The XML is also shown in the log and the attribute is called "support_inherit".
+1 vote for a few free months for renaudg. :)