You could have a loose connection anywhere in the circuit and it may be difficult to find. Or, it may be a loose connection at the breaker, as you alluded. Start there.
If you (the homeowner) are not what the National Electrical Code (NEC) would describe as a 'qualified person' (generally, a trained
electrician), consider that there is probably a lot you don't know about sticking your hands inside electrical distribution panels, splice and junction boxes -that could injure or kill you or inadvertently burn your house down.
If you are not skilled at making electrical splices, there's no point in searching for a loose one.
The job of the qualified electrician is made all the more difficult by the well-meaning but, unqualified and unskilled who attempt to do electrical work in the residential setting.
The last person who touches any part of the electrical system owns it. That means when an electrician is called in to do some kind of work and performs it properly, when the house burns or someone gets hurt, it matters little that Uncle Charlie, the amateur electrician had his hands in there first and may have performed sub-standard work that caused the loss of life and / or property. When things go wrong, everyone is a defendant.
Which is precisely why I always shied away from residential electrical work. In an industrial setting, no unqualified people are allowed to touch electrical equipment.
The main point is this: work with electrical circuits should be respected as a life safety issue, which it is. The purpose of the NEC is for the protection of life and property and should be strictly adhered to.
Be careful who you take advice from. You wouldn't take financial advice from someone who is broke. Be leery of electrical advice from those untrained in the trade. That goes for electrical engineers, as well. They know the theory but may not be skilled or knowledgeable about the trade (wiring installation and maintenance methods).
I hope that makes sense.