Hi,
I’m using MikroTik hAP ac3 with PPPoE for WAN connection and as I’ve read somewhere about performance decrease from mismatched MTU so I’ve figured out that adjusting my MTU everywhere from default 1500 to 1492 will be a good idea 
It improved nothing and now even though I’ve reverted all the changes I’ve made back to 1500 BUT some servers straight do not respond to a ICMP ping now (e.g. https://thegamer.com/, https://xda-developers.com/) and are unavailable via browser (I’m getting just ERR_HTTP2_PROTOCOL_ERROR and browser console shows just no response from the server). Any idea what would be the debug steps now? How to identity and fix such an issue? Not even sure where to start, is there any kind of logging I can enable in Mikrotik to see what is going on?
I’ve tried mss clamp rule like add action=change-mss chain=forward new-mss=clamp-to-pmtu passthrough=yes protocol=tcp tcp-flags=syn but that did not fixed anything and also after some forum post to check fragmentation with sudo hping3 -p 443 -S -y -d 1460 thegamer.com but I’m not sure what this is supposed to achieve because it’s not an ICMP ping and uses just port 443 and on top of that and it’ll max at 1500 because it’s the maximum I’ve set on the router.
EDIT:
Not sure how/if that is a relevant information but after checking all the IPs that are not working all of them resolve to an Amazon AWS hosting in the US
52.5.96.96
52.203.114.80
44.196.161.176
3.222.90.168
(https://ec2-*-*-*-*.compute-1.amazonaws.com)