All exchanges are doing wash trading including Coinbase and it is interesting that this comes just after Coinbase announced they should get listed in stock market.
I am reading that this was related with their trading in period from 2015 to 2018, and imagine what the situation is now with much bigger volume than before.
Interesting to read this short CTFC report and some former employee of GDAX was doing this:
https://www.cftc.gov/PressRoom/PressReleases/8369-21
No doubt Coinbase needed to get this matter wrapped up as part of their IPO preparation. You can't go to market with an unresolved regulatory matter against you. This is further reason that crypto exchanges need to be regulated though. It's too easy to game the system if their actions aren't monitored.