Phone shows -70dmb in signal but always 1 signal bar?

hi guys. I have an annoying isssue while using AOSP or CM-based roms. I have a m7vzw. The signal is good when i use sense or GPE rom, but with aosp and cm, my signal bar always show 1 bar, sometime it even drops to 0. I checked phone status *#*#4636#*#* and network type is global, signal strength is -70dmb, ASU 255 (or 225,i dont remember). In battery history chart, the color of signal on is orange-red (while GPE and sense shows green,which mean good signal) and has little spaces like they were dropped to no signal

i dont have screenshots right now because i restored my backup, but i can re-install if needed
Is there anyway to fix it? i switched to GSM in preferred network but it doesnt help. Also i still have H+ data (my country doesnt have LTE yet)

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