I ended up resetting 1 of the 4 P100's. Updated the firmware then the other 3 upgraded without any issues. no router reboots were done. This sounds more like a software issue than anything else more...

@Angus1972 Same here I have 4 x P100 v1.2 that will not upgrade from 1.4.5 to 1.4.9. Seems like Tapo/TPLink have some issues with upgrades and have yet to address this issue.