Try disabling the Power Saving feature added in the 10.5 OS update and see if it helps your issue. (or at least will eliminate as a possible culprit.)
Settings/System/Power/Power Savings/Auto Power Savings 20 min. (Uncheck to Disable).
This feature has reportedly caused some unexplained quirky behavior to some devices when enabled.
Otherwise, the device may either be overheating (maybe check if it is hot when this occurs), or experiencing some memory cache issues causing the reboot. Normally don't see rebooting when experiencing network issues. Usually a setting, a Channel/app or physical culprit.
If still experiencing issue after changing the above setting, see if occurs on certain Channel/app or across the board regardless of what type of content you are watching.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102