Newly downloaded macOS Server 5.6.3 for High Sierra throwing codesign errors

I am in the process of moving a Mac from macOS Sierra 10.12.6 to High Sierra 10.13.6. I am also attempting to move my Server application to the corresponding level, which is 5.6.3. The clean install of High Sierra works fine using a fresh download from the App Store. The latest version of several old OS versions are now available with updated certificates so it makes sense to go this way.

As for the Server app, the App Store lets me download the last compatible release, which is 5.6.3 as expected. When I launch the app to begin setup, however, it immediately crashes with the following termination reason: "Namespace CODESIGNING. Code 0x1." I've managed to play around inside app package to figure out that several pieces of the app are throwing these errors.

Here's where things get a bit curiouser. I have a second Mac that's already been on High Sierra for about two years. The only difference is that I had installed an earlier version of the Os and then applied the combo OS update. I can download the 5.6.3 version of the Server app from the App Store, and it will launch fine. Both Os installs are current through the 2020-005 security update and thus report the same build of 10.13.6: 17G14033. And the downloaded version that I received from Apple was indeed build 17G66, aka the last version of 10.13.6 prior to subsequent security updates beginning with 2018-002. With those updates supposedly being cumulative, the only difference appears to be the incremental versus combination application of the patches, but that's somehow enough to produce this Server app problem.

Anyway, I am in a bit of a hard place to know quite what to do next. Unfortunately, for a few different reasons, I no longer seem to have an earlier archive of High Sierra to install to rebuild this other Mac in the same way as the first one. Nor am I confident that I can hack my way through the code sign errors, meaning that it's Apple's job as developer to fix them. Judging by my time today with Apple Support, however, I did not sense much enthusiasm for that.

My post here is a mostly cautionary tale for others. While I didn't find a similar DB post in my search, I am sure there must be other users out there who have or will stumble across this same same issue. We all need clean installs now and then. But I am all ears in case someone else has a workaround to suggest - thanks in advance.