From a PC, try playing your App - not preview-playing it in the Power Apps Editor - but by playing it for real i.e. getting a URL like
by pressing the Play button on make.powerapps.com under Apps.
Then, try pressing F12 on the keyboard.
Then, on the right, click the Console tab.
Then, try the operation again which triggers offline data to sync.
Does any error show up? If so, please share it here.
from same PC, please try all of the above again from the beginning, except press the Network Tab on the right this time instead of the Console tab, then do the operation again. A new line in the network tab should appear and it should be red, at the same time as your error message 'Name Could Be Too Long' shows up.. Highlight this and then share details what was the status code of the HTTP request, the return value of the HTTP request and anything else of note.