[Q] Preferred network mode won't stay on GSM/WCDMA/LTE on Lollipop 20e

Every time I change my network mode to GSM/WCDMA/LTE (Auto) it goes back to GSM/WCDMA (Auto) after an hour or two. I can get LTE in my area and I do after changing the network mode setting manually, but after an hour or two my phone goes back to GSM/WCDMA and I loose LTE. I've tried going into the test menu and choosing my preferred network mode but it won't stay. My build.prop file has not been edited. I don't have the LTEconfigs.apk to delete.

Any ideas on what to do?