From one day to the next, the secondary machine started to work really bad, no matter which compression settings i choose (High color quality, 60 fps, and 70 image quality or low, 30 and 50, respectively) it suffers a lot of lag. The primary machine has ethernet connection, while the second one has WiFi connection, I tried switching it and doesnt work. Any solution? thanks
Routers can cause lags and latency. Bypassing them always improves performance.
This does not only apply to USB Tethering, but also to direct ethernet cable connection and WiFi Direct connection.
If your secondary device is Android, you can try connecting via direct Android USB cable.
Please refer to the chapter Direct USB Cable Connection (Android only) in the user manual https://forum.spacedesk.netuser-manual/#item_11689.