The following are the issues I have noticed after upgrading my Asus Zenfone Max to Android Marshmallow:
Battery drains faster than it used to in Android Lollipop.
GPS fix takes a lot of time and does not stay for long. Navigation does not work in Google Maps due to this.
I would request Dev team to fix the issues ASAP.
As I rely highly on GPS navigation, and there does not seem to be a fix for GPS issue, I would like to roll back to Android Lollipop.
Just to add to the issues that I face,
I have some 2700+ contacts and they dont pop up fast enough to make a call, even the search for the contact does not display the results fast.
Have to clear the memory every now and then to access the contacts.
Faster battery drains
Unable to move the apps to the SD card for RAM space
Apps take longer for launching
zenfone max got an issue whenever I turn on my wifi with 4g on, it reboots my phone and keeps bootlooping, it doesnt automatically cut off the 4g whenever I turn on my wifi connection, end up resetting my phone and taking out my 2 sim card then turn back on my phone before I can off my wifi connection on my phone, then off my phone again to insert my sim card again to use the 4g.