VPN hacking?

Hello all!

Configured LT2P over IPSec so I can connect to my home from anywhere. Generated strong passwords for user and ipsec.
Time to time I get lot of such firewall logs

input: in:lte1 out:(unknown 0), src-mac 00:0a:3b:0b:71:74, proto UDP, 35.193.182.105:4500->212.3.210.4:4500, len 196

They vary by len, and this is before something like this kicks in:
phase1 negotiation failed due to time up 212.3.210.4[4500]<=>93.174.95.106[4500] e5f858a0876af576:c22664dc33ff2c4a

Should I be worried? Maybe some additional firewall rules should I add?

You can add port knocking to keep your vpn locked down.
https://wiki.mikrotik.com/wiki/Port_Knocking