Due to a bug in Safari, it will keep forgetting your saved login. I reported it to Apple about 2 years ago and (as sadly appears to be typical with reporting issues to Apple) they are yet to do anything about it.
It shouldn't cause you to lose work though. You can save your project regardless of your login state.
Using other browsers won't help, because Apple banned all other browser engines on iOS, so those are just skins for Safari.