Switching between characters results in a
"Got Duplicate LOGIN_SUCCESS".

Never got this in my two years of ST:O experience...

Should I be worried and change my password, or is this an issue that may be caused to to lag (EU to US)?

I also got this error today logging in for the first time since the patch today- not after switching characters. I'm in the U.S., so we can rule out server lag.

I am also concerned it's a hacking thing.

Got this first time ever last night while loading an old unpublished project in the foundry editor, it bounced me all the way back to the loading screen suggesting I submit a ticket. I simply relogged and the error never reoccurred.

so no answer to this then?

I got the same, and my first thought was concern over my account being compromised. I got no email alerts and it only happened once. Since I was able to immediately re-login, I think it's more likely a glitch related to LoR.