I have an issue with my mikrotik RB750 v6.43.4 been using this firmware for approx 6 months and everything was working fine (I am green about these routers) now I am experiencing 100% cpu usage and internet disconnections.
there are 2 other routers that are connected site to site pptp to this router (however when disabled the interfaces cpu usage remained 100%) so I am guessing they are not the issue as they have been configured for about a year.
Any ideas what to check or fix?
Hello,
Since v6.43.4 a lot has happen and also some CVE has been fixed. If you are on Stable release I would start with changing to Long-Term Release and upgrade to 6.43.16
If the issue still continues I would export config, read though so there is nothing strange in the config (you have been hacked or so on), netinstall the device and import clean config.
If the issue still persists then you might need to dig deeper into it. I think it will be quicker to first upgrade then netinstall before you try to dig deep as it will be quicker and if you go to support they will tell you to do it anyway. 
after a lot of tries managed to get it updated and till now seems to be working fine. Thanks.