Clarification is here.
So, “The current patch is from May.”, which means the June security patch level given in the install guide is wrong, until /e/OS 3.0.3 is released with indeed the June security patch level.
So, the brickings shouldn’t have happened because of Android rollback protection.
It is now unclear why the brickings happened, anybody having bricked their phone have not done anything wrong, it would seem.
Apologies for suggesting otherwise because of the initial looks of the issue.
The current solution to the topic still applies … contact Fairphone support!