Installed 2018.1.1 on my old IBM Celeron machine, but left 2016.3.1 on the HD. Had multiple problems with Terrasync.
Specifically, for example, took forever to download KFWA (Fort Wayne) scenery area, and after 1/2
hour of grinding away, scenery never loaded. Constantly outran scenery when crossing boundaries;
and had to pause simulator for it to fill in, etc.
On hunch uninstalled 2016.3.1. Fort Wayne downloaded many times faster; then rapidly
loaded. Terrasync functioned correctly as of old.
My speculation is that the 2018.1.1 start routine may create redundant cache files, if 2016.3.1 stays on the HD, thus eating up the limited cache available with Intel on-board graphics.
If that's so, no telling what other evils may arise; so best not leave 2016.3.1 installed. Best regards
to all.