Waitforme I think it gets in a tiz sometimes, when it does that, I often find it’s best to close the page and reopen it. Theres 2 things Flarum on free hosting doesn’t seem to like.
Whisper (the real time pm system), very resource intensive, only use if absolutely necessary. It will stop any potential spammers though.
Some of the buttons in the editor for uploading images. I got rid of one of the troublesome ones, the other I can’t.
In green are the methods that work best. At the moment I am having trouble with the image uploading tools as well for some reason. The one that always seems to work is direct linking to an image hosting site and simply pasting the direct link into your post. I use https://imgur.com/ It always seems to work, is free and doesn’t seem to have any real limits on the images you might want to store for uploading onto the forum. Strongly recommended.