It's not about the engine (interesting concept your argument, to speak about it later-on, IF time), but about the layout.
Detailed example has already been given since the start of this topic (see abobe, posts No 1 and 3).
According to this layout, 4 groupsforums should be headed by 4 titles, each placed (according to miniBB instructions) BEFORE a specific forum (the 1st at everyone of the 4 groups).
But, instead (as already said), only 2 out of 4 groupsforums'headers/titles appeared (the other 2 were never seen !). The first header/title would not accept to be placed before the 1st specific forum. Worse : the second header/title was "arbitrarily" placed before another specific forum, different from the chosen, and it appeared impossible to reasign it to the desired place.
"Finaly", after wasting a whole night, we found out that the first header/title would only start after a 2nd forum (may be for esthetic, presentation reasons). While the second header/title seemed to be "sticking" into a specific forum (different from the desired-one), whatever changes you might make.
To bypass the obstacle, we had to re-name this "sticky" specific forum, and push all others after it, in order to get at least the second header/title in a useful place.
But, the other 2 headers/titles for the rest of the 4 desired groupsforums (3rd + 4rth), still remain ..mysteriously "Missing" !
(NDLR : As "4days" suspected, it's not excluded that some strange interferences during transport of minibb files -i.e. bb_specials, etc- might have negatively influenced a part of the settings. Indeed, as we found out later, our www connections -and/or computers- apparently faced some kind of abnormal electromagnetic perturbations/aggressions which seriously affected minibb's setup in general, and even ..destroyed other machines
By the way : Does miniBB have some bullying "big" Competitors ?
However, the Forums' "Structuring" problem remained even before and after these strange, exceptional, negative interferences).