When you see an fcs error it is almost always the cabling on the radio at the other end of the link from where you see the FCS errors.
You can change cables over and over again on the side where the FCS occur and have minimal results.
It can be a bad cable from media converter to Mikrotik, bad media converter, the problem with fiber optic cable between 2 media converters, port on neighbor device and of course port on Mikrotik.
Way to go about this is to change everything until the problem stops.
1. Change utp cable between Mikrotik and media converter
2. Use a quality cable and quality connectors (we avoid the easy connectors). Be careful not to over crimp, or not to kink the cable.
3. Be sure to secure the cable with a tie at the radio to avoid movement of the rj45 connection.
4. Change port on Mikrotik
5. If you own media converters, change them.
6. if the problem is still there screenshot your logs and send email to your ISP so they can check everything on their end.