Why is Ubuntu suddenly asking for loads of memory and not starting (under Hyper V)

I installed ubuntu on a Hyper-V virtual machine. I allocated a minimum of 2Gbs mem and initially I had not specified a maximum. My desktop (host) has 16Gbs memory and loads available.

Yesterday, everything was working fine and I saved my ubuntu virtual machine state. When I tried to start the virtual machine, it kept failing on memory allocation... According to Hyper-V, it was asking for 13Gbs while I only had 12Gbs available.

I finally managed to start the virtual machine by deleting the saved state and capping the memory to 4Gbs (although it seems to still use 5Gbs)

What might be the reason for using so much memory?

PS: I have not installed anything beyond the base ubuntu installation because I could not get networking to work anyway...