Of course SSD firmware is buggy. You know why? Because any half-decent electrical and computer engineering team can slap a NAND flash controller and some flash chips on a PCB, take the controller's manufacturer's reference firmware implementation, tweak the dozens of knobs provided by the reference implementation (ignore FLUSH commands, change the amount of reserved sectors, disable this, enable that, etc), change the device ID strings to "Company Foobar SSD 2000", and release the product on the market, with minimal QA and testing. And that's exactly what happened in the last 5-7 years with dozens and dozens of companies around the world designing SSDs.

But with traditional HDDs, the amount of engineering and domain-specific knowledge to manufacture and assemble the platters, moving heads, casing, etc, is such that there are only a handful of companies around the world who can do this (Seagate, WDC, Hitachi, etc). They have decades of experience doing that, so the firmware part of HDDs happen to be very robust as these companies have seen everything that can and will go wrong in an HDD.

So it boils down to this: which would you trust more, an HDD firmware code base that is 20 years old, or an SSD firmware code base that is 4 years old?

Combine this with the fact SSD firmware is much more complex (a flash translation layer must minimize write amplification, do wear leveling, spread writes on multiple chips, etc), and you are guaranteed that many SSDs on the market are going to be very buggy.