When running
execute store result <storage location> int 1 run function <function location>in a function the output will be stored for every command executed in the called function except for commands starting with "return run".
With the attached datapack applied when running the bug:main function the output is stored for the first 2 "random roll 0..100000" commands even though those commands aren't prepended with "return run" and the output of the last "random roll 0..100000" command isn't stored even though it is prepended with "return run"
Can confirm.
Related to MC-262027, which describes that the return value of /return <value> command in a function cannot be stored without storing the values of all commands in the function. This issue describes that the return value of /return run <command> command in a function never can be stored directly like other commands.