A bit of peer review and refactoring later: This patch will fix the typerror and make scheduling work in media forms without needing to patch core.
jvollebregt-swis → created an issue.
The problem is that instead of just saying "We support {n} facets in the url" this module uses up as many as possible. This is a problem in building the menu because the url parameters are also stored in 255 chars but core adds some more stuff to it first putting it just over the limit.
Technically this is core's fault but if we're willing to limit the number of filters we can have active at a time we can work around it by lowering the maximum length. For us 240 was low enough to stop the error but this patch sets it to 200 just to be safe. (This only allows 22 filters enabled at a time, but I figure that's good enough)