the wallet always wants to update Witnesses addresses, but unfortunately the wallet does not save the addresses... Could this be the problem?
No, this can't affect the speed.
One way to accelerate sync is to enable the bFaster option in your conf.json. This file either already exists or needs to be created in your data folder (the same folder that contains byteball.sqlite). The file should look like:
{
"bFaster": true
}