The rider who had the above problems also ended up getting put back onto the ship in Tunis because he played the long game with the police up to the point when the shift had to clear its workload, so to speak.
There is a long version here:
https://www.youtube.com/watch?v=_z9Uzg3bKks
I can't say I watched it all but it seems you now need an actual stamped receipt – 'voucher' – from a hotel (which will be checked up on) before they stamp you a visa. Plus a return ticket and reservations for your entire stay.
Booking.com confirmations will not do, even if non-refundable.
Afaict, with help from a local, he got the voucher delivered to the port at the last minute and was let back off the boat just in time.
A French rider with a faked voucher was sent back.
Passage through Customs will also be expedited with small presents.
It doesn't have to be anything extravagant.
I remember this from the pre-Arab Spring days at La Goulette; setting about unloading 8 bikes from a lorry before they lost interest.
It seems the requirement for these incentives is now stronger.
Tunisia was the only country in North Africa which ever played these games which are normal south of the Sahara.
If you're heading for Tunisia it may be worth watching the whole vid.
Or
read more about voucher
It is possibly all to do with how Italy classifies Tunisia in terms of Covid risk, and that may change after March 15.
Ferrying from France has far fewer restrictions, even on the same ferry line.