The bans given to Martinius Stenshorne and Nikola Tsolov are the first of their kind in F3. Arvid Lindblad also received a fine for unauthorised GB3 testing.
F3 says racing in similar series (GB3 and Eurocup 3) on the same circuits where F3 will be later this year is an unfair advantage and therefore forbidden by F3 regulations.
That is probably the reason why this rule exists. It didnt exist back when people like Max and Lance were coming through, and you can guess that certain kids were getting lots of private tests when others didnt.