Hi to all users,
RB951Ui-2HnD, ROs 6.45.8

I can't ping other devices, I can't ping RB from other devices, no TCP/IP available from inside, I can access to RB only through Winbox-MAC
I supposed there could be something wrong with OpenVPN server (I run OpenVPN server on different RB, same board model and ROs version) but in this case I have just a router.
Reboot: not solved.
Removed all firewall rules: not solved.
As further test I removed all entries in ARP list: this solved issue.
How to debug?

Thanks.

Looks like something is wrong with TCP/IP config.

As further test I removed all entries in ARP list: this solved issue.

ARP should be a very dynamic list, of IP-address/MAC address tuples, based on ARP requests and responses. Is the ARP setting on the interfaces anything other than "enabled"?
Other possible ARP/MAC problem is after restoring a backup from another device, which contained the MAC addresses from that device. ("Reset MAC address" should solve that one)

For debugging ... you have tools "TORCH" and "Packet Sniffer" to see what happens in that router. You have tool "Traceroute" to see how the packets are routed.

ARP entries were all "dynamic".
Router was correctly working, I haven't loaded/restored/imported configurations....

OK, focus on "route" now.
Pinging from or to same subnet ? Then there is no routing needed if subnetmasks are correctly defined.