Mackie Mixer Troubleshoot

I have an older Mackie 1642 VLZ Pro. I run the Control Room out to my amp and on to my speakers. The main out I run directly into my sound card for recording. Just recently the Control Room volume knob has started to act funny. When turned all the way down there is still plenty of sound bleeding through, and at certain low level volumes some of the signal drops out (sounds a bit like its being filtered). Once i get to about 9 o’clock on the dial it seems to sort itself out and sounds good.

One other clue is that the output meter is lighting up two ticks like it is registering a low level signal, but no audible signal or noise can be heard even at max volume.

Any thoughts on what might be happening and what to do to fix it?

thanks!