If your LEDs were in parallel and you have tried to replace dimmer one with no change, then problem is resistance.
Resistor of 30 Ohm with low tolerance (20% - no 4th band) in 3V parallel setup could mean 10mA change (20%). But, it shouldn't be so dimmer.
Other thing could be bad wiring and soldering which could add to resistance.
So, disconnect battery and measure resistance from battery connector to LED, then on resistor. Other wires and resistors should be reference points.
With battery in place you could measure voltage drop on LED, then on resistor.
BTW. if you don't have multimeter to do measurements, you could check soldering points for some higher temperature. This could mean bad soldering and higher resistance.
Good luck