I have noticed after adding https, that I simply can not submit my URL some places or my RSS feeds because the https prefix is not allowed. Is there a reason for this that I am unaware of?
When you say "the https prefix is not allowed" what do you mean by not allowed? What's it actually saying to you? Do you have screenshot or something to try?
I have a theory and think it's because before https existed the platform you're trying to submit to was only coded to handle http so all it knows is that there is a problem with the url.
Some sites and platforms are very slow to update to handle the new https url. Therefore it just fails on you saying that it's not allowed or there was an error of some sort.
It's like how when the new TLD's came out like .club some places wouldnt even recognize it as a URL and not automatically hyperlink it like Skype and forums do.
But now a few years later Skype and most places recognizes most of the new TLD's and hyper text URL's like www2 www3 http http etc now but its a similar thing.
You could message the sites in question owners and ask them about it but am sure they'd probably say the same thing and thusly prove my theory correct.
The problem is, for some places, such as RSS sites which are usually custom coded, this costs money to do and is why some are slow to catch up and fix it!