It's not a single phone. device issue. My HTC One m9 has the same or similar issue except it latched on to the 1X800 or lesser quality signal as primary in SCP, but also shows some LTE. I am on Lolliop 5.0.2 PRL 55025.
Both screenshots below are in areas near towers with SPARK / Bands 25, 26, and 41 service fully functional.
In fact, the very towers identified ARE SPARK / Bands 25, 26, and 41 service fully functional
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I tried one day to do the airplane on / pause / airplane off system bmoses and others and suggested. My m9 became a worse power hog after a day of doing so. After doing so, the m9 would run hot due to the CPU or memory increased activity. This was true even a few days after doing it when not doing it for a day or two. I ended up doing a soft reset to get the battery drain issue resolved. I am not so sure that I will be doing the airplane switch much due to the battery useage and the device running hot aftermath that lasted for days.