manufactured JLC PCB trace/connectivity weirdness

[src1989]

I designed a 5V LED PCB (The BigClivicle), which flashes LEDs with a PIC micro. I've so far assembled about 50 of these without a problem.

this one icicle has such a problem: several of the segments don't light at all, or sometimes they light dimly.

initially i thought it i'd cooked the LEDs or the PIC by keeping the iron on too long. replaced them. problem persists 

transplanted the "dud" PIC and LEDs to another PCB, and they worked perfectly. 

thought it could be flux residue; cleaned it off with IPA solvent. problem persists. 

re-did the solder joints. problem persists. 

bleeped the traces out and everything connects where it should, and nothing shorted... 

what can i try next?

[DavidAlfa]

Just don't bother saving a cheap pcb?

[Kim Christensen]

bleeped the traces out and everything connects where it should, and nothing shorted... 
what can i try next?

You must have missed something. Check it using "ohm" mode instead of the "beeper" mode. A low ohm resistor (33ohm) will "beep" and a high resistance one (100K) will not beep, giving you a false sense of confidence that all is OK when it's really not.

[n4u]

Maybe you provide high resolution image and show us. Maybe there is less soldermast and u short sth when soldering ?