Cannot load any study after loading 5 studies successfully

[AllLuckBased]

I have 12 studies I wish to load to practice. I have been facing a lot of issues loading most of my studies. 5 studies have loaded successfully at the moment but now I cannot load anything (either with PGN file or with lichess study link)

When I try to upload PGN file it says the error 'Syntax error at line x, character: y; Unexpected: "null"' where x & y always refers to the end of the file. Here is a screenshot:

I know the PGN file is good as when I load that same PGN file into a lichess study it loads seamlessly.

When I try to load the study from an existing lichess study, it does not give any error, but the board is smaller and none of the chapters/moves seem to have loaded:

I hope someone can fix this issue, as I love the opening practice that we can do on this website.

[ArneVogel]

Can you share the pgn you uploaded?

[AllLuckBased]

The PGN files that I have uploaded so far were all very large PGN files with only one single chapter, since I wanted the algorithm to switch between any line of the opening. The original study on lichess has all these lines separated into many chapters, but I wrote a program to merge all these chapters into 1 chapter in a PGN file.

The PGN files are correctly formatted I assume, since when I test the same PGN files on lichess it loads seamlessly. But for some reason it gives 'Syntax error at line x, character: y; Unexpected: "null on listudy. It might be possible that lichess PGN reading algorithm is a bit more fault tolerant and it is handling some small syntax error on the background but I cant tell if that's the case.

Here is the PGN file(in .txt format since github says it does not support uploading .pgn files):
Slav Defense (White).txt

Also you can view the buggy study on listudy after I loaded it there:
https://listudy.org/en/studies/6mgmu0-slav-defense-white

Sorry for the late response, I did not check github for a while.