Looks like it's coming back! Was probably just a shed.
I've been told Minoxidil likes to get lots of hair on the same growth cycle, so you can shed a bunch at one time if they are all on the same cycle and they should come back together.
I've also read people saying that minoxidil loses its effect after some time and then people lose their minoxidil gains. However I believe that's usually because people stop their regimen or aren't on finasteride, or finasteride didn't work for them.
There are definitely long term users of finasteride and min that gain and keep over years and years and years.
I'm almost a year into my treatment (Big 4, biotin, collagen, etc) and I have sheds but have only trended upwards.