I've been having a similar issue for the past few weeks. I have the latest app update on a Moto e4 plus (republic wireless) running nougat 7.1.1., that just got the most recent security update.
In my case, if/when I get a notification it's usually late by half the time remaining. Rarely I won't get any notification, and occasionally it will pop up several minutes after the auction closed. Some items I may be watching to see what current selling prices are and won't care if it's finished... but if I intend to bid, it's a PITA to miss buying and have to go through a new search with the possibility it will all happen again.
I don't have any battery saver apps or features turned on at all, and I've toggled the notification switch for eBay several times this week already, so no joy there either. I also explicitly exempted the eBay app with the phone's data saver options for WiFi to cell switching, so there's no interuptions with service.
