I went through the steps to backup my configuration and update to the 1.0.0 OctoPi release just to be on the latest and greatest. Before that I was running the previous version of OctoPi with the latest version of OctoPrint. I've been running on the same 3B+ for a while with no issues related to power supply. However, with the latest OctoPi, I'm now seeing undercurrent warnings with exactly the same hardware. It doesn't make a lot of sense to me, but I'm wondering if the way that is determined somehow changed?
Unless this user also explicitly confirms they started using OctoPi 1.0.0 and suddenly started seeing undervoltage warnings, then it is not related. People have undervoltage warnings all the time, and it is a coincidence that this post was at the top of the list when you looked.
Fair enough. The coincidence was interesting timing.
In my case, I've been running with this hardware for at least a year, so the only thing I can attribute the new warnings to would be the update to the underlying OS in OctoPi 1.0.0 versus the previous version.