The update was from 2.6.18 to 2.7.3 for testing. After the update the information for Online Banking are missed. I had to rearrange the mapping to the Gnucash accounts. After correcting this I restarted Gnucash. Then I reconcile with my bank account. It takes all transactions I already reconcile in the past. This happens if you choose "Last retrieval date". at the first time you have to choose the last date before the update or nearby then it works. Those informations should be insert into the Release Notes.
I believe that had to do with Geert's relocating .gnucash/ to XDG_CONFIG_HOME and that it's now resolved.