Ungrounded systems are MOY open circuit to ground and you should not expect that. The Earth/bonded system even if it’s just sitting on concrete is still a conductor, however poor. Bonding just keeps the impedance low. AND the insulation is a very high resistance but also it has capacitance. The definition of a capacitor is two conductors separated by an insulator, any insulator, even a vacuum. A capacitor blocks DC but passes AC.
So your system is now capacitively grounded. But since you don’t and probably can’t control the system capacitance to ensure it is perfectly balanced the current across each phase to ground is slightly different. So owing to AC Ohms Law or V = IX the three voltages are never equal or necessarily make sense. In fact due to the way it interacts with arcs, the voltage to ground can get up to 600-800% of line to line voltage during an arcing fault. Since arcing faults have much lower current than shorts breaker/fuse tripping takes a lot longer: in the mean time it does a lot of damage (arc flash) and the excessive overvoltage surges shred motors in the first couple turns.
As others said you lost your grounding. This is like a floating neutral...finding it isn’t easy.
