Since KSP 1.7.2 empty continers spawned in an assembly space collide with it.

[allista]

[LOG 21:20:59.229] [DIY Kit: Flex]: Ready to Launch - waiting to start physics...
[LOG 21:20:59.229] 6/26/2019 9:20:59 PM,AmpYear,OnVesselCreate
[LOG 21:20:59.235] [000_AT_Utils: 21:20:59.235] Vessel assembled for launch: DIY Kit: Flex
[LOG 21:20:59.319] [Dynamic Battery Storage]: Summary: 
 vessel DIYKit (loaded state True)
- 0 stock power handlers
[LOG 21:20:59.537] [FlightIntegrator]: Reloaded drag cube for zeroed cube root part DIYKit on vessel DIY Kit: Flex
[LOG 21:20:59.538] [FlightIntegrator]: Vessel DIY Kit: Flex has been unloaded 1.79769313486232E+308, applying analytic temperature 176.292893558036
[LOG 21:20:59.735] [USI-LS] Vessel situation changed, refreshing life support
[LOG 21:20:59.736] [USI-LS] Vessel situation changed, refreshing life support
[WRN 21:21:00.632] [F: 80515]: Vessel DIY Kit: Flex crashed through terrain on Mun.
[LOG 21:21:00.634] DIYKit Exploded!! - blast awesomeness: 0.2
[LOG 21:21:00.636] [DIYKit]: Deactivated