Yea,its been pretty dormant for awhile.How often do you power this thing up? That really matters, as Windows 10 will do all sorts of "housekeeping" including Windows Security scanning on a machine that's long been dormant and needs it.
But you need to get off of Version 1803, which is long out of support.
Doing a Windows 10 Repair Install or Feature Update Using the Windows 10 ISO file
Then, seriously, what you experienced is what is to be expected on first power up after a very long nap.Yea,its been pretty dormant for awhile.