It seems by your comments that your colleagues are using the code review process to agree a methodology or polish the code. I have just started to do code reviews like you and I notice that sometimes we discuss a lot over things that are just implementation approaches or improvements. This is not bad at all as far as its reasonable (300 comments look too many for me, that must look like a reddit thread)
Maybe you need to agree some architectural decisions about the code before start implementing it or maybe is just agree about naming conventions, patterns and good practices so you all know what it is considered "good code".
If you are complying with your code standards as you say and the code works as intended, there shouldn't be so many comments, so either they are using your code as a forum or they are trolling you as it seems that you are pointing.
I would try to be critic with myself, would try to take part in the conversations and see the reason of all this comments and maybe talk with them about it in a constructive way to see why are they so unhappy with your code and if you can code in a way that makes everyone happy and the work don't get stuck in code review.