cavity discovery flaw, seen it many times in millbox/sum3d going as far back as 2012. never seen it fixed. no idea how to fix it. shouldn't make a big deal for fit and finish. click the 1mm toolpaths, you should see it finish just fine.
Hi, in that case just send backup project to your cam supplier to give change to check/analize that behaviour. However, remaking (automatically or manually) the preplines will automatically recreates the dark grey cavity cap too.