Tracert isn’t the best troubleshooting tool in this case. Tracert sends a UDP packet with a TTL value of 1, then 2, then 3, etc. The nodes along the way may or may NOT send a “Time Exceeded” ICMP packet back to you. Thus, the timeout entries you see are likely because a node doesn’t reply rather than a node is offline.
hit-and-miss website issues can be DNS problems. You’d have to start with a problematic PC. What DNS servers are they using? Yours, others?
The web browser error message is best place to start.
If it says DNS problem, try pinging the website. Does it respond?
If it says can’t connect, use wireshark on the PC to see if the web server is replying. You can also capture packets on the Mikrotik to see if packets are going out, and if any are coming in for a given connection.