iPhone shows charging indicator, even when off power

My iPhone 12 Pro Max, following upgrade to iOS 16.6, showed the charging indicator symbol (battery with a lightening bolt) all the time, even when it was not connected to a power source. In overnight charging on an Apple fast-charging pad, it failed to charge beyond 73% where it previously always reached 100%. Changing to a working regular Apple charging cable failed to change this condition. The indicator continued to show the iPhone was charging, but no actual charging took place on either charger, and continued to show the iPhone was charging when it was off power. Only leaving the iPhone off-power for several minutes finally resolved the issue, at which time the battery indicator resumed its normal function, both when charging and when disconnected from power, and charging resumed normally as well. While the issue is resolved, I remain concerned that it may happen again, and would like to understand it’s cause(s) and how the issue may be avoided in the future.