Just reverted back. Doesn't happen there.
Starts immediatly, and from what it seems, goes faster in exporting.

Please report to adobe as well, they need to fix it!

For what its worth: since the update to lightroom classic 12.0 every problem I had seems to have been gone.

Still, for those who experience slow export speeds, to try to turn off 'use GPU for export'. My export times doubled when that was on.

Thanks for your feedback!