3 hours ago, ritterss said:

According to your advice, i deleted the Player & Headtracking comments mod entirely, loaded the save before opening the door to the church, prior to talking to Debora. The Player & Headtracking comments's effect is thus disabled, as my character doesn't turn head towards Debora while she speaks. However, the issue persists. When we are teleported to the Stein's hideout, the 3d person camera switches between Ivy, Stein and my character, but after few lines it goes into 1st person view and is stuck on Stein. Then the scene plays as before: after the cutscene there's fade-to-black and nothing happens. Please advise.

Sounds like the scripts for it are still active in your save. also fully deleting mods outright during a playthrough will introduce other issues.

You can try the ForceEnablePlayerControls command in the console.

Applied this console command in the Stein's hideout. Gained the control back, able to move, but the issue persists. The screen goes FTB and nothing happens😶

4 hours ago, ritterss said:

Applied this console command in the Stein's hideout. Gained the control back, able to move, but the issue persists. The screen goes FTB and nothing happens😶

When the quest is done, a video is supposed to play. If it doesn't it could mean the codecs aren't there on your system. Remove the video file from the directory, that way it gets skipped. 

Fallout 4\Data\Video\ivy_credits_bik.bik

You can double click the file to see if it actually runs on your system too. If it doesn't and you want the proper codecs, download Bink & Smacker here: https://www.radgametools.com/bnkdown.htm

Just keeping you updated. All worked eventually. The thing was that there were NO video file with credits in the game directory. Apparently, the game was trying to play back the file which wasn't exist in the system. I just unzipped all DATA folder from the mod into the game as required and all went perfectly. After the credits we appeared in the Stein's hideout, safe and sound. Thanks for the clue redarding the videofile.

So, for the record, for the future generations of players who might encounter the same issue:

Have Player & Headtracking comments mod turned off or removed prior to entering the church, you may enable it after the quest is complete;
Have ForceEnablePlayerControls console command handy, just in case if you are stuck during the last conversation;
Thoroughly check the mod's integrity, make sure all files are present
 

6 hours ago, ritterss said:

Just keeping you updated. All worked eventually. The thing was that there were NO video file with credits in the game directory. Apparently, the game was trying to play back the file which wasn't exist in the system. I just unzipped all DATA folder from the mod into the game as required and all went perfectly. After the credits we appeared in the Stein's hideout, safe and sound. Thanks for the clue redarding the videofile.

So, for the record, for the future generations of players who might encounter the same issue:

Have Player & Headtracking comments mod turned off or removed prior to entering the church, you may enable it after the quest is complete;
Have ForceEnablePlayerControls console command handy, just in case if you are stuck during the last conversation;
Thoroughly check the mod's integrity, make sure all files are present
 

You'll want to NOT unpack the sound files. There are .wav files in the build with predefined loops, that won't work if they are not in the BA2 file. If this needs to be done, unpack just the video file.

But this is all a workaround for the fact that a BA2 file did not run on your system. The best solution is just install the right codec.