When I try to select a region using shift+arrow, if I hold the key combination down for a second or two it will continue selecting the text after the keys are released. It appears to enter an infinite loop and only stops after reaching the end (or beginning) of the buffer.
The arrow key alone does not show the same behavior. This is reproducible across major modes.
Using GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.14) under WSL 1.