"The connection to service named com.apple.lsd.modifydb was invalidated"

I have a MacPro Mid 2010 5,1 running 10.13.4, Boot ROM version MP51.0089.B00. I noticed the problem about a month ago when I would be in normal mode and the computer would crash after attempting to do two things at once, like have the internet open, then open a random app...the pizza wheel would spin and I'd have to press the power button to bring it back up. The problem got quickly worse so that every time it would come back up, it would crash after a few minutes. Going into Safe mode however and the Mac seemed to be fine. I checked in Activity Monitor and 'secd' and 'lsd' both took up over 120% of the CPU. In Console I kept getting the continual message "The connection to service named com.apple.lsd.modifydb was invalidated". I noticed that the Security Update 2019-002 10.13.6 was available so I tried to do the update thinking that this might help, and although it would go through the motions of downloading and restarting, the Mac was still in 10.13.4 with the update still in the 'Updates Available' area of the app store. I then booted into Recovery Mode and ran Disk Utility and ran First Aid on all my volumes and everything came back ok. I also used my original start up disk and ran the extended Apple Hardware Test, and after an hour and half, it came back as okay as well. I also tried to install the Combo version of the High Sierra, but this also either did not help or update the computer. Finally tried a PRAM and SMC reset, in addition to a virus scan, which also came back as clean. Now run out of ideas I thought I'd do a clean install of High Sierra so I wiped my SSD (which I use for the OS and apps) and my HDD (to store everything else) and reinstalled it using a USB backup. With just High Sierra installed, and nothing else, the computer would work fine, no issues at all. So I decided to bring back everything from a Time Machine backup from over a month ago (when I believed my system was running okay), but it's back to the same constant "The connection to service named com.apple.lsd.modifydb was invalidated" message in Console with Activity Monitor Showing CPU usage at over 120% for 'secd', basically right where I started again. A call into Apple offered no help since they said I've done pretty much everything that they would have suggested. Is there anything else that I can do?? Please help!!