Use this forum example:

1. Go to search page by user:

https://asmbb.org/!search/?u=methuselah

2. Search result show invalid url => 404 not found (the 0 is rendered as o):

https://asmbb.org/does-anyone-else-smoke-pipes-here.27/

when valid one is:

https://asmbb.org/does-anyone-else-sm0ke-pipes-here.27/