Is the 'backup' function failing or the 'restore' function?
The maximum number of tasks per action is 8, the overall maximum number of tasks is 64. I have just tested on a CueCore with v1.27 and it works okay over here. Can I suggest you do a 'factory defaults' reset via the Cuety tool to 'format' the memory of the CueCore; perhaps something got corrupted. (I usually advise this when upgrading between firmware versions.)
best regards,
Maarten