There was a related bug report about this a while ago regarding finalpacks, however the bitpack download file link has the same issue, where using the # symbol breaks the bitpack.

Here's a recent OHB using the # symbol for the bitpack filename:
https://battleofthebits.com/arena/XHB/5311/

The link on the page does not work, however this one does:
https://battleofthebits.com/disk/battle/00005311/XHB05033%20Sega%20Genesis%20ExMO%20%233.zip

(this is done by replacing the 735 in the url with %23)