This used to happen a lot, under certain circumstances. It hasn’t happened to me personally in the last content patch or two (primarily, since inquis burn was nerfed into the ground). But it was server-side, and very noticeably so. Desync is a packet loss problem. That does happen very rarely, and it’s my own connection. It does not happen often, maybe a day out of a month, and is related to my own internet connection.
I’m not going to say my frame rate isn’t lower on a populated map, or during world bosses–but the last 2-3 world bosses I attended, my FPS was completely fine. I’m in Klai right now and my FPS is stable, 60-65.
Turn off dead parts, 100% of the time, on all characters. This is the likely culprit for frame rate drops in CMs.
If you’re still desynching or losing frames during Rainbow Trek, I’m not really sure what to tell you, perhaps restart the client right before doing it as the game does still have a memory leak and suffers the longer it’s been open.