Bhall was resurrected before BG3 when Viekang and Abdel fought about(over?) 100 years after the events of BG2. The events in Throne of Bhall appear to be noncanon (The Solar, being the last Bhall spawn etc)
Viekang was a plot hole in ToB anyway, since he had a good chance to suriveve the events regardless.
I do actually have an idea to explain the discrepancies:
If the Bhaalspawn rejects godhood, the Solar takes the taint from Gorians Ward and Imoen and seals it in ( i think) celestia.
The spellplague damages the the seal and the taint is slowly dripping back. Imeon is weakened during the spellplague and a mad Viekang kills her. And later attacks the last remaining other Bhaalspawn and whoever dies gains the full essence and turns into Bhaal.
If the Bhaalspawn accept goodhood, s/he becomes a lesser god and scrambles for faith. During the second sundering, AO takes the godhood away and the former good reincarnates as a mortal again. Viekang, still alive, is driven mad by the return of his taint and attacks the Bhaalspawn.
Both are just headcanon, but I do kinda hope Larian inserts some hints, how ToB and Murder in Baldur's Gate are connected.
..Maybe Amelyssan herself explains it to us..
Argument against Imoen: The Absolut does not have an obsetion with pink.