So i was out on my bike racing this weekend and i had a pretty fun time but on one of my practice runs my chain fell off so i quickly got off and put it back on and worked perfectly fine from there. However, when i got home I was just cleaning my chain and then it suddenly kept on slipping when back peddaling! This only seems to happen in easiest 3 gears (i only have one chain ring in front) and although it does sound like it's my de-railer, it seems to be severely cross chaining which has never happened before! I have taken a look at my cassete and my front chain ring but neither seems to be bent or broken! Any idea how to fix? Link to videos and photos here - https://drive.google.com/folderview?id=1eHtjKAPuN_xKHlyJ4q3OdK5cRmVeDUWV
Hmm... 1x drivetrains will put the chain in extreme lateral angles, so back-pedaling issues are common.
But you know your bike and you seem to indicate that you did not have back-pedaling issues before.
So I would start troubleshooting by ensuring that your derailleur hanger is not bent - there are tools to gauge and align the derailleur hanger.
Also, check your chain for wear and tear - maybe it's time to change it.