OpenVPN: ping in remote network does not work from --up script

Question

18.04.5 LTS (Bionic Beaver)

OpenVPN 2.4.4 x86_64-pc-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] built on May 14 2019

What works: