iPhone 8 experiencing cellular problems.

So there’s a issue right with these day. I used this phone like 2 years now and LTE signal just started to acting weird 2 days ago. It disappear and appear again continuously. I got a very strong signal a short period of time and quickly got weaker and weaker and changed to 3G. I went to the local carrier store and they tried on their phone it is receiving LTE signal without problem don’t know why. This form is quit similar to my issue 4G not working on iPhone 8 plus - Apple Community

I wonder if anyone can help me :v