On your other devices, start the new “log in” process (“Add Profile”), select “Add as Seconds Device”.
(This will result in these second devices having two instances of the same profile)
When successful, delete the original (duplicate) profile on your secondary devices.
“Add as Second Device”, as well as transferring a backup, will transfer the whole profile database, which includes the relay list.
The reason why the devices didn’t sync for you is because they just have nothing to connect to each other over. If the relay wasn’t down yet then the new relay list would get synced.
By which you mean “delete delta’s data and start anew”, correct? There is no way to delete my data directly from delta? Like, on debian I would be deleting ~/.config/DeltaChat/ and starting the application again?