system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can a cell phone receive a 4G, 3G, 2G, 1G, and no signal in a short time (10-15 minutes) without physically moving location or orientation?
gpt
A huge Pokemon-Go raid appears near your location

But seriously, there are a lot of factors that can play into signal reception.  It could be the weather, a network issue, something about objects/obstacles between you and whatever tower your phone is trying to connect to, the number of other users nearby and their data usage, internal phone operations and power consumption, and network-specific issues occurring within the tower network backbone.