@Pras71 do you use VLANs?

  @RaRu I know that there was a recent update to the router firmware and an update to the OpenVPN app. Do you think there is any correlation?

I use this app: https://play.google.com/store/apps/details?id=net.openvpn.openvpn

  @infinitytec 

I use the same app.

I didn't have any update for router recently, but it's true that my mobile VPN app got updated...

I'll try to find some APK file with previous version of that app, install it and test then...

did a test here against the ER605v2 and an ER707-M2
both failed against my android phone. same config from PC, vpn worked against both routers.

I also tested android against openvpn on an openvpn server running linux, there was no problem with android to that server.
I don't know where the problem is, maybe android has blocked tp-link's old and outdated openvpn, i don't know..

  @MR.S @infinitytec @Pras71 

I confirm, on 3.3.4 works like a charm!

Looks like newest Android app update (3.4.0) is an issue!

OMFG, I've waisted for that like a 4 whole days and bunch of already done configuration. FFS.

  @RaRu 

I do a last test to a unifi router, same client same phone, no problem what so ever.

the problem is only to tp-link routers.

  @MR.S 

My question now is. Shall we wait for move from TP-Link? Or OpenVPN (mobile app creator)?

  @RaRu 

good question, I don't know where the error is, I just know what I have tested now.
​

and my test shows that it works against all openvpn servers except tp-link. so !!