I agree with the other posts insofar as that is very difficult to remotely troubleshoot this type of problem in a forum absent the config. You can look in "/tool profile" to see what process category is causing the CPU spike. RouterOS does not list out the individual processes but only the categories.
/Tool -> Profile pointing to firewall.
For me it's quite a difficult to understand why load are rising slowly. In any case kernel failure should not happen.
We are going to do an experiment, will transfer same config to old CCR1036, if behavior still will be same - definitely problems in config.
Also, it is possible problems occurred in flash/NAND.