Clients in same WLAN can't reach each other

My bug report might be misleading now though. I wrote it because of the problem caused by some characters in the interface names. After i renamed the wifi interfaces i never had such problems anymore, my Archer C5 has more than 200 days uptime today (still on 17.01.4) and works prefectly fine. Also LAN ←→ WLAN always worked for me, only between WLAN clients was no connection.

As far as i understand it, most people here experience a different bug, that comes after a somewhat random time and that affects different wired/wireless combinations.
It would probaly be helpful to try the workaround that Jow suggested here:

To make sure that it is really caused by this feature.