Ensure Castle.exe is added to your Windows Defender "Allowed Apps" list. Disable Fullscreen Optimizations: Find the Castle.exe in your Steam folder. Right-click > Properties > Compatibility . Check Disable fullscreen optimizations . 🏆 The "Pro" Workaround: Steam Remote Play Together
If the lag stops, have players one-by-one raise their resolution to find the "culprit" whose PC cannot handle higher settings. Disable V-Sync: Every member of the party must set Vertical Sync to OFF online fix castle crashers best