Check the Functionality of your Plugins
I like to give a quick reminder that it is very prudent that you check your plugins once in a while if they still behave as they should, especially, after each major WordPress update.
I had in the past some big issues with one of my websites until, Kyle, personally, did solve the issue and I was so thankful.
Back then, I had a plugin which prevented copy and pastes so no one could copy the content of my site etc. It did work well for over a year and after WP had a major update it failed. I couldn't see my newly posted post only got a blanl screen when checking it out through the preview.
Someone, then, in the WA community told me to check out my site by going incognito on Google and, yes, there was now post.
Well, long story short, it was this Copywrite plugin and Kyle deactivated it and everything was back to normal.
Therefore, I have a certain routine when it comes to WP updates like saving everything first and deactivating all the plugins. After the update is finished, I re-activate one plugin after another to see if it is still functioning with my site.
However, there is still the possibility when you can't check everything and by everything in my case, not writing a comment on my posts.
Most of my comments, so far, are coming from WA members through the SiteComment and, there was never an issue. Makes me wonder now why that is?
Nevertheless, a friend of mine, outside of WA, wanted to leave me a comment. She was so frustrated because, so she said, after clicking the Submit button, the only thing she got was a white screen.
Well, this raised my eyebrows and I immediately started my research by going incognito on Google and voila, I also received a white screen by trying to submit a test comment.
I knew instantly which plugin it might be who causes the interruption and, after deactivating it and checking it again, everything was back to normal.
Wordfence, this time, was the culprit which I had installed before the major update of 5.0 and it did work fine. Now, it is deactivated and deleted.
Sometimes, a plugin can go crazy after a major update and it might be not compatible anymore with your theme or, even the update of your theme might cause the trouble.
The bottom line is, take the time and check your plugins. Write even a test comment on one of your post/page, at least, don't panic when you experience a white screen or another abnormal issue, always check your plugins it is usually one of them.
Take care and have a great week ahead