If you have a heat gun you can use low setting and pry them open carefully that way, otherwise I'm pretty sure you can bake at like 225 for like 10 mins and they will open. Make sure you use good butyl sealant putting them back together.

I have no experience with those headlights but unless you are sure the ring needs extra solder, you may want to swap the rings out with a new set, they may have a defect.

To me it sounds like a bad connection so your solder theory may hold weight, since you replaced the LED controller for them. Check your connectors too and see if there is a bad connection somewhere.

Either way I think you have to open them up! Take your time and go slow, those shouldn't be too bad to open.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards