TeX Live and MacTeX ⇒ problems with PDF after updating MacTeX

[kinseikun]

Hello all,

First I must preface that I do not know much about LaTeX. I have been creating my textbook and updating it for a few years now using LaTeX but I do not know the in and outs.

I recently got a new Macbook and thus needed to reinstall MacTeX even though I migrated over all my applications. I am running Big Sur on the new machine while the other one wasn't even updated to Catalina.

Now my PDF output is awful--I have horrible spacing issues and paragraph numbers I had put in the margin one day was on the wrong side, and today even though I have not touched it, now they are in the middle of paragraphs. I noticed that the old machine is using a 2017 version TeX Live and the new one is using a 2020 version.

I have no idea how to get my PDF back to normal or what the issue is. Attached are screenshots of the spacing issue--one from the old version and one from the new.

Any help is appreciated. I don't think it should be normal for me to have to find out how to redo the spacing every time I update...