I observed that if you add a new map and while adding you do not change the default name that appears, the loading issue does not come.
Afterwards, you can rename the map.
Have you tested all routerboards or specific ones?
RouterBoards are using Level 2 logic circuits, giving basic level 2 switching at wire speed without packet loss (i can confirm this as i tested it with a professional Ethernet Tester at 1 Gbps full duplex).
Sorry for typo......in the above config put disabled=no
/ip firewall filter
add action=drop chain=forward comment="ping block" disabled=yes icmp-options=8:0-255 \