One specific redirect doesn't work

[Eworm]

I have a lot of redirects in a client site, but one specific redirect just won't work. The source is /plus/kostenlose-kurse. If I change the source to wout for instance, it works, but not with this source. I refreshed the stache, cleared the cache but nothing.

Statamic: 3.4.7
statamic-redirect: ^2.7