Let me make this clear up front: I suck at punctuation and grammar and fortunately I have an Amazon echo to help me with spelling... so I'm a bit of an expert on bad PG&S.
Lately I have started to read stories (here and elsewhere) where the punctuation and grammar need a lot of help.
I take into consideration that this is a global community and many people are writing in a second or even third or fourth language from their native tongue. I am in awe of you folks, truly. To actually sit down and write in a language other than your own is a skill I can never attain.
So I do try to look at punctuation and grammar problems thinking about this (and also, having a profoundly dyslexic sister I take that into consideration too that there are writers here who also have this to work with.}
All that said, might I offer that big problems with punctuation and grammar do make it hard to read a piece (I've stopped with several) and can, with some readers, affect their reaction to the work. There is a reason professional publications ask for well formatted and punctuated work. It also shows a degree of professional attitude.
There are ways to correct problems; from the program you use to write with to asking for readers to help you with those things specifically. I rely greatly on my beta readers to help out there.
I also tend to contact writers via private message about such issues instead of making remarks in their comments section.
Just a thought.