Thank you for the info. This is actually a non-syringe kit it comes in a pre-inoculated substrate and is supposedly ready to go. The company also supplies all the buckets and bins. In retrospect I may have been better off controlling the environment from ground zero using my own substrate and inoculant. So much for taking the "easy" route I do agree that it is possible that airborne contaminant was the issue - but all four bins seems unlikely. I probably would have been less annoyed had they been helpful rather than sending a form letter with a 60% off coupon - almost like this happens all the time. In this case the company has every financial incentive for the first batch to fail so buyers must purchase a second batch.To be fair, contamination is not customarily the fault if the vendor.
Further, unless the contamination has begun to bear spores it is exceedingly difficult to distinguish contamination from legitimate mycelium.
Now unless there is a common vector such as a contaminated instruments poorly washed containment (probably not an issue given your post) or free flowing highly contaminated air (or water I suppose) then I posit that your syringes were originally contaminated.
I always test syringes using agar. I am not suggesting you do this but I only state it as explanation. I have had on multiple occasions, contaminated spore syringes.
Now at what point did you initiate fruiting? Did you do so before your substrate was fully ccolonized? If you did not then infection is a certainty.