There is entry in journalctl
Mar 16 12:14:10 r14 systemd[1]: /etc/systemd/system/frr.service.d/override.conf:7: Unknown key name 'LimitNOFILESoft' in section 'Service', ignoring.
it was implemented for T5045
https://github.com/vyos/vyos-1x/commit/cb872efb5b8dac9c9095502bbb14e858d07dfef3