They are connection limiting. At times. Correction - their CDN's are connection limiting. Probably primarily around new event / assailant times.
With all accounts logged out, bring them up one at a time - at some point some will start getting the error. (Next time, load in a different order, and you'll probably see each come up successfully, then stop around the same number. i.e. it's a connection / internet error, not something within your home. If, say, Plarium has 1,000 connections to that CDN, and you come in early on, all will be well. If you're near the max, sometimes you'll get in, before someone else, sometimes the reverse.)
"Connection error" and "Connection lost" have nothing to do with you / your connection - either their code blowed up your browser and it reset that tab, or there is an error between -their- servers and -their- CDN. If you can get to the internet, you have no connection issues - it's them.
Solution: Run a proxy addon. (Or run a VPN.) Come in from different IPs / CDNs.