I have a trashcan 2013 Mac Pro at work with this problem. I've had it for a few years and upgraded it through multiple macOS versions as well as cruffed it up with various versions of McAfee endpoint protection etc. So I assumed the issue was a result of some of that cruft and decided to wipe it out and start with a fresh install of high sierra over my holiday vacation. The day after doing so the same issue happened again! At this point I called Apple support for my long out of support mac on xmas day and to their credit they not only helped me on a major holiday, but did so quickly, kindly, and without ever asking me to confirm a serial number to tell me I was out of support. Luckily for me the issue happened again between contacting them and collecting log files for them to look at so they had legit logs to review. After escalating the issue and having engineering look at the details of the case they came back to tell me that it was a known issue that they were working on. They were not able to tell me what is causing it, or give me an ETA on when it will be fixed if ever, but I'm at least glad they are aware of it. I know the trashcan has been basically left for dead with regards to updates, but hopefully they care about it enough to at least fix known issues like this. I can always downgrade to Sierra, but I'd prefer to stick with the latest OS in the hopes that it will be fixed soon. Fingers crossed.