IndexError: list index out of range bug?

[Larz60+]

I can't see where you are incrementing rownum, you haven't shown that code,
but as I previously stated, it most likely has to do with index starting at zero.
thus if you keep incrementing rownum, at some point it will be equal to length of frame + 1, thus returning an index error.
if you surround your code with:

try:
    ... your code here ...
except IndexError:
    print(f"Index error, rownum: {rownum}")
    raise

this will show what rownum is equal to when the index error occurs.
Also, you should always post your error tracebacks, complete and untouched as they almost certainly pinpoint the cause of error.
(Use error tags)