I have a same issue. vpn ipsec passtrough not work. If you use latest firmware 0.9.1 1.2 v004a.0 Build 180502 Rel.53881n ipsec passtrough not work at all.
If you use some earlier beta version. Ipsec passtrough work somehow unstable. It falls down often. I had written to tplink support center. No answer.

So today only solution what somehow worked for me is with beta firmware. See the link below https://forum.tp-link.com/showthread.php?94393-problem-with-vpn-passthrough-in-Archer-MR200
Archer MR200 v1 I think hardware is ok but firmware development to this model is pretty weak.

First the issue is regarding an MR400 V1 EU - not MR200 - my mistake.

I discovered when in VPN, via the MR400 to my home VPN server/router, one could only see the MR400 NW infrastructure on the Client. I do not know why, but perhaps the MR400 should use my home router as DNS.

I then realized that my home router and the MR400 shared the same IP adress (DNS-issue?). Setting the IP for the MR400 to 192.168.0.1 resolved this.
I can now Access the NAS on my home NW (via the MR400), but Windows/mac will not willingly display these recourses in the file manager (DNS???).

As many mobile nw Suppliers no longer offers you a Public IP for Your router, I set a specific APN to Ensure this. Unfortunately i did not verify the MR400 "public" IP before I made the change, som Im not shure if this is relevant here.

Conclusion: Both my routers had the same IP - not good. Cause may be DNS issues. Resolving this in one way or another should fix the problem.