I also have this problem with LG Zero H650E. Android 6.0. I raised the data measurement warning line, but still the hotspot is being randomly closed. Has anyone found a solution?
All the phones work. I use them occasionally mainly of sentimental reasons. The older phones are dual band and work on European GSM 900mhz/1800MHz bands. The newer phones work on European 2G / 3G /4G bands.