If you are still using CoRE, please update to the latest version as soon as you can. Here’s what changed:
v0.3.16e.20171219 - RC - Replaced recovery safety nets using unschedule() with a much more optimized method that does not affect ST as much as unschedule() does
This is important as CoRE has been identified as a major choke point on a certain method that it uses (ST describes that as expensive in their documentation. As it turns out, it is. With ST’s help, CoRE is now able to recover from timeouts much faster and with a lot less resources than by using its own recovery safety net. You should also consider moving on to webCoRE instead, as CoRE is no longer actively maintained and only gets critical updates.