Game don't login when using Wireguard

[MUSTANG]

Hello.
I've set up my home router with Celeron N3160 To work with one of the common VPN services using Wireguard protocol. Everything works just fine except the Alchemy Stars game. It just won't log in and shows [6,-1] error. When I've tried connecting via OpenVPN protocol and everything worked but the speed was twice as low (110-140Mbps vs 250-300Mbps). Also, there aren't any problems when I use this VPN service via their app, including manually choosing Wireguard protocol in it.
Any ideas on how can I fix this?

[MUSTANG]

Problem solved by setting MSS on Wireguard interface