Win7x64, KSPv1.7.3 Steam, no DLC, mods: KIS, ModuleManager
Steps to reproduce:

1. attach Ground base to the ground
2. save-load
3. move kerbal to check if GB is still attached, if all OK, continue, if not, reattach
4. save-load
5. get CB1 Ground Base detached or exploded due to crash into terrain

In case of detach in save file (quicksave#2 in attached zip) somewhy parameter staticAttached at
VESSEL[CB1 Ground Base] {...
PART[kis.concreteBase1] {...
MODULE[ModuleKISItem] {...
becomes set to False.
In case of explosion (quicksave#4 in attached zip) vessel somewhy is saved like it flies:
VESSEL[CB1 Ground Base] {...
sit = FLYING
landed = False

Savegame & log:
KIS bug.zip
KSP.log.zip

Found an interesting string in KSP.log:
[WRN 23:02:19.866] [Part:kis.concreteBase1 (CB1 Ground Base) (id=F2290957939)#Module:0] A static joint has just been broken! Force: 2476.839
after loading quicksave#1. So this is the reason for staticAttached = False in quicksave#2.

Also looks like explosion occures even before the part was unpacked.