Their can be many causes for these issues and they can be due to assembly issues, a defect or water quality so this will be tough to narrow down without more info.
1) Cease use of all stress coat, dechlorinator (you should be using RO water anyway) and any vitamin or amino acid supplements as well as medications, aiptasia or slime algae treatments for a couple weeks. Basically, if it is not calcium or buffer or a trace mineral, do not add it as organic additives can cause a skimmer to either not skim, skim what is seemingly just water or alternate between the two. We want to rule this out and not using them for 2 weeks to see if the skimmer function improves is the only way.
2) The skimmer must be correctly assembled, be sure the pump is clipped in to the skimmer, that no loose or damaged parts are present, the pump should start easily and make no unusual noises, the gaps (seams) where the front and back half should be even, if they are not a cord or hose may be in the way or some stray casting marks may be obstructing the unit from closing properly, usually this can be forced together but some quick work with a file or sandpaper where the seams are not 100% would be the best solution. The only openings on the pump should be the impeller well at the top and the round intake in the front that plugs into the front housing. Their is a hole on the back underside of the housing that should be plugged by a clear cap, make sure that cap is present.
3) Make sure the water level stays fairly constant and it is set ideally when you see a steady cascade of water into the intake with no struggling or surging of water level, basically it should look like a smooth waterfall of water coming in. The skimmer should be installed in a relatively calm area with no strong flow aimed directly at it.
4) Make all adjustments slowly, one of the biggest problems we see is constant tweaking, set it and leave it alone and make adjustments in small increments 1/4 turn at most and wait at least 6 hours before making another adjustment even if this means dumping a couple cups of clear liquid. The smallest adjustment can make the difference but it may not show the result immediately.
5) Watch for patterns with the bubbles, if they get worse the longer the lights are on, the issue is likely oxygen saturation and algae or fast growth of soft corals or new cold water for water changes are likely culprits. If it happens after adding buffer or calcium or kalk, an excessive KH and high CO2 can be the issue.
