I know that this is the total transactions and not profits, and the numbers are way, way off. I have a local copy of all my trades, of course, and they match perfectly with the transaction history available on GDAX. But the numbers that Coinbase reported on this 1099-K are completely wrong. They literally put the wrong numbers in the 1099-K. And as one would expect, dealing with Coinbase support is about as much fun as being set on fire. I fear that Coinbase is going to end up costing me a lot of time and money because of their botched accounting.
[1] https://www.irs.gov/businesses/understanding-your-1099-k