Use a recording app called glip see if that works

This may be due to the battery settings of the recording apps, for a possible solution go to settings then scroll to the Apps section this should show all of your apps then find your screen recorder app and press it then you should see the app info find the Usage section and the second option on the usage section should be "Battery" press that then you should see the options of Unrestricted, Optimized, Restricted press the unrestricted option so android doesn't automatically close the app in the background, this should fix the problem so you can record your speedruns let me know if this fixes the problem.