That is strange, I’ve not come across that before (and cannot reproduce the issue). I have no solutions, but some questions…
Is it the case that all stations disappear, or just ones you have recently added?
Are these stations that you have added via TuneIn or your own URL, or are they from Roon’s database?
When do they disappear? - after a reboot or restart?
Do albums that you add disappear too?
Has this problem started recently?
It doesn’t sound as though this is a radio station issue, more likely something specific to your setup, and so I think this would better posted in #support.