Help please !

My kitchen floor has a linoleum covering and is about 6 years old. Recently it has lifted in small "bubbles" near, but not immediately next to the junction with the kitchen units. (The lino extends underneath the units but not fully to the back wall). On a couple of the "bubbles", the surface has clearly been broken, although no-one, including my teenage sons, can tell me why. (I did suspect cigarette burns, but I have been assured not). One of the holes is leaking a grey/white-ish liquid... not a lot, but say 1/4 teaspoonful, every day. I suspect that the concrete below has de-stabilised.

a) What is the likely cause of what is happening and why has it suddenly started happening ?

b) Have I any repair options ?

c) If I replaced or repaired with more lino, what is to stop the problem re-occurring ?

Many thanks
Rosie