Not unusual when you try to rotate and manipulate the plug since there a sliding contacts inside. Avoid playing around with the plug like that. Just make sure it's firmly inserted in the charging jack.

Also not unusua to see flickering under heavy load when battery must occasionally help charger adapter meet high CPU/GPU power demands. During these times battery is actually draining even though plugged in.

Once battery drains below about 50% level, charging the battery takes precedent over CPU/GPU power demands. Then stuttering starts and FPS/game performance drops. Time to stop playing to allow the battery to re-charge to 100%. Gaming can then continue until battery again drops below 50%,

This is why battery should be 100% charged and plugged in BEFORE starting heavy loads for maximum play time. If you don't stop gaming and fully charge the battery when it drains below 50%, the charging light will continue to flicker and performance will just keep oscillating every few minutes between high FPS and low FPS as battery charges just above and drains just below the 50% level.

Unlikely the way you described it. Sustaoned CPU temps about 90*C or less are OK under load. GPU about 85*C or less also OK. Brief excursions above those temps aren't that critical. Sustained overheating above those temps usually manifest by stuttering videos or freezing or BSODs or shutdowns, not flickering LEDs.

Sure it's possible. Ask the tech to re-seat the connectors.