Sounds like a bad connection to me.
And this is dangerous. This could set your house on fire.
It happens all the time with backstab connections that a poor connection creates a virtual "fuse" that "burns out" above a certain current (often well within the rated ampacity of the circuit). This results in a dead branch. It would be less common, but certainly not impossible, for such an "accidental fuse" to be self-healing; making it an "accidental circuit breaker".
The problem is, such things cannot be counted on to be stable. This is likely to devolve into a more serious arcing fault, which can create hundreds of watts of heat in a near-pinpoint area of the receptacle. This can melt the receptacle, and even set the box or surroundings on fire. It's a big cause of house fires, and the reason AFCI breakers are Code for most circuits today. AFCI breakers listen for the electrical sound of arcing. (if you've ever jiggled a headphone or speaker wire and heard crinkle-crunch, that's the sound, and it manifests both electrically and aurally.)
Don't overload the circuit
A gaming PC. Those have "850 watt" power supplies - but that's on the DC side. You still have to count efficiency and power-factor, so if you look at the AC-side nameplate, that typically says 10 amps. But all the cool kids today are using 1300W supplies that AC-nameplate at 15 amps.
So you're putting that, and ~1A worth of UPS (figuring battery recharge current), and 12.5A worth of heater... on a 15A (typical for bedrooms) or 20A circuit.
All but the UPS need a 125% derate, so over 30A provisioned, all on a 15/20A circuit.
This is treating wall outlets like a cornucopia, and that doesn't work. I expect what's been happening is this "accidental circuit breaker" has been preventing you from overloading the circuit, and so your actual circuit breaker has not tripped. But you must fix the bad connecton, and when you do, the breaker will see full draw, and likely, you'll get trips.
Best tocall an electrician and have them fit a dedicated circuit (or two or three; the hard part is the fishing; tossing in an extra cable or two is no trouble) to support your hardware. Bedrooms are simply not wired for big PCs and heaters. And if you want heaters, rather than buying a rinky-dink $20 heater-fan every year, heck, in 2-1/2 years you've paid for a proper 2000W baseboard heater ($50) that'll last 20 years! So have the electrician install that on a 240V circuit.