Help! Switching predicted ovulation dates

the app has just shifted my ovulation days and fertile period back by a few days so it now says I’m due to ovulate now rather than in 4 days... I think it might have been after I inputted some bbt data and OPKs. Not that any of these were positive yet and but my temp has gone up quite a bit. Does anyone know why it would suddenly do this, especially when my OPKs weren’t positive other than one last night which oddly was v v close to positive (they’re now mid negative results)...

Thank you for your help!x