I think there are two possibilities either a loose connection or interference (which will cause signal quality to drop. As you’ve checked the connections, one thing to do is to keep a note of when it happens. This might enable you to narrow down the cause.
For example, if it happens at the same time then it could be a a unsuppressed water heater turning on. Other things to look out for are the motor of an old fridge as that will give out massive amounts of interference when it kicks in. Any fluorescent lights and so on.