When dr strange defeated inbetweener he was backed by lord chaos and master order... The inbetweeners masters.... Ibs powers are based upon balancing all things
After defeating him the masters sealed inbetweener in the nexus of realities where all things are already balanced. Inside that realm ib was sealed in a special prison that was unbalanced so his powers would still work. With thanos help they battered the prison and freed ib who then found himself powerless in this odd realm where law and order meet