Are you using a universal Bluetooth connector with a keyboard connected to the same Bluetooth dongle as the mouse (I.e. like the Logitech universal dongle)?
And finally, are you connected to WiFi on a 2.4ghz frequency?
I ask these questions because if either of the last two are true, that could be the issue. My Logitech MX Master sometimes has issues if I am using the universal Logitech dongle with a Bluetooth keyboard at the same time, and it can have issues if I am connected to a 2.4ghz frequency too. Connecting directly to the MacBook’s Bluetooth and using 5.0ghz frequency WiFi fixes the lag I sometimes would get with my mouse too.
I believe I found the issue. It seems using my monitor as a pass through for the mouse was the issue. Connecting it straight to the computer via dongle seems to have solved the issue.