Could be a multitude of things.
What were your dosages and cycle length?
You need a modified pct schedule if you ran deca.
Typically running Testosterone 2-4 weeks longer after last Deca injection. It's not set in stone. Many don't do it or have not thought about it.
Deca takes a little longer to clear your system.
Also Testosterone dosage needs to be taken into account.
Someone running 1 gram of Test may need a little longer for Testosterone to have adequate clearance.