BOD > COD help

Hi guys, forgive me in advance for not having a wealth of chemistry knowledge! I work in a chemistry lab largely testing water (drinking, irrigation, tradewaste) and my main job is doing the BODs (5 day). I am having a lot of trouble with 2 of my samples, both from the same town. A nearby abattoir has released its waste into this irrigation lagoon, and since that happened the BOD always exceeds the COD. Protocol for me dictates that I retest it after getting this result, and typically it falls back under the COD result so clearly something is happening in the week that it is in the freezer to bring it back in range. We cannot report a BOD that is higher than the COD (which seems odd to me since clearly there’s something going on that needs fixing?). It is always the same 2 samples, and I’m wondering if anyone had any insight into why this might be happening. Also, not sure if it’s of note but I am not able to add a nitrogen inhibitor since that is a different test under our methods.

Any help would be greatly appreciated!!