Thank you Buba68. Here is a followup .

After killing the guards, all the MT denizens were hostile. Even though that fight leveled me up to lvl 5, I reckoned it would be impossible to defeat them all in that state. So I went back to an older save. Before we entered the bridge. Mizora reappeared, Now I just agreed to do her bidding without asking to liberate Wyll, and after that, the loop did not occur anymore. So I could get in, and free Minthara who was there (hanks for the info Buba68).

The previous time there were also exlamation marks on Wyll and Karlach, probably to followup on the Mizora dialogue and the successful request to end the pact, but now these weren't there. Maybe there were just too many dialogue options stacked that made the thing go wrong.

I could talk to the dead Halsin in camp, but all he could tell me was that the tadpoles were ambedded in magic and that the source was in Moonrise Towers. So maybe, this is why they make him appear in the camp if you avoid him in act 2. To give you that info if you use speak with dead.