Just use journalctl (without -b) to see all messages (they are
still in RAM in the journal - as per the log you posted, journald
will use up to 80 MiB [2] which is more than enough to keep all
3000 or so messages). Just look through them (there are going to
be a lot of debug messages from udev) and look at the timestamps.
There you'll be able to see where the delay happens - and maybe
you'll have a chance of figuring out, what the problem is. If
it's nothing obvious, just post the last 20 or so udev messages
before the large gap in the timestamps and every udev message
afterwards. If there is no gap and udev is constantly doing
something, take a look at what it's actually doing.