I work in the IT industry specifically in web server administration. Please reply to this thread with information regarding the internet provider that you have issues with. I have noticed if I switch to wifi hotspot on my phone the issue tends to go away. I am posting this thread and poll to see if we can get some information together that the mods can take to the server providers and administrators to help resolve the issue.
The types of issues that I have seen that only to affect users that attempting to post and not so much when trying to read posts that are already made it seems to be consistent with POST attack mitigation techniques that used.