I grew up in Ashland (visiting there right now, in fact) and have family who funded one of the first marijuana companies in the state.
Some problems were bad behavior from legal growers, but I'd argue the bigger problems were caused by regulatory and oversight failures from OLCC and enforcement of existing laws on illegal grow operations.
1) OLCC allowed for way too many grow license at first. For a state of 4.3 million, you have a serious upper bound to how much the legal market can support. There was some discussion about weed tourism, and a bit of work to allow legal interstate sales between Washington and California, but nothing really materialized.
2) A plant could produce $500+ in product, but it cost tens of thousands of dollars per acre just to get your plants in the ground. That's not including harvesting, drying, trimming, and storage. Given that there's no crop insurance, if anything goes wrong you're easily a couple hundred thousand in the hole.
3) OLCC often added regulations mid-grow, after it was impossible to effectively respond. This included things such as dropping the batch size for a test (which costs hundreds of dollars per run) down to 10lbs per batch. This sort of uncertainty, the oversupply of licenses, and the huge up getting operational costs made it financially impossible for a lot of farms to break even. I don't condone it, but I do understand why a lot of folks under reported yield and sold part of their harvest in other states.
4) A lot of the truly bad actors we're organized crime rings moving in (Russian mob and Yakuza from what I heard). They got a hemp license and grew marijuana illegally (usually having a few hemp plants in case a state tester came to the grow site). Local law enforcement knew about it, but they were literally out manned and out gunned. The feds eventually offered support, but it took a while. Folks understandably freaked out, but OLCC mainly used the mob as a pretense to try to wrestle hemp regulation away from the ODA (which they have been trying to do for years) rather than acknowledge that this was an enforcement problem, not a regulatory problem.