In case you are using some clone of APM2 FMC board the most recent version of firmware you could be able to flash is 3.2.1 and not 3.3.x. So I believe you mean 3.2.1. https://github.com/ArduPilot/ardupilot/blob/master/ArduCopter/ReleaseNotes.txt (search there for "drop support for APM1, APM2")
It needs to be explained on more details what exactly do you mean as "i loss control on throttle". How exactly does it looks like?
AltHold automatically keeps drone hovering at constant altitude in a middle position of throttle stick.
If your drone needs really high throttle value for hovering in stabilize mode then you may have not enough throttle for hovering drone in a middle position of throttle stick. So drone may go down immediately after you switched it to stabilize. The same time it will respond ok on roll/pitch actions. Is it your case?
Also you receiver may have failsafe features and here is a chance it could provide some "safe values" to FMC in case of signal loss. For some receivers there could be "presumably safe values" of controls implemented, for other receivers a "last received values" could be used. Once you turned your transmitter off, receiver may detect it and use failsafe feature to keep drone in air.