Had similar problems with the so called Neo6 GPSs myself, and quite often others report issues here.
One GPS that does work well is the Quectel L80, small and not expensive. Never had problems with those I have bought on Aliexpress.
One issue was noted with the Quectel L70, so may impact the L80 as well, they stop working at an altitude of 10,000m, when they should not when set to balloon mode. A genuine L70, bought from a trusted source in the UK, did work correctly at 10,000m+.
I do sell bare PCB breakout boards for them, you can add components to power down the GPS etc.