I don't know about what happened before with your parents changing your citizenship (though I find it hard to think possible unless you were under 18 at that time).

That the company won't give you the paperwork to get a Z working visa is a red flag. If you will be working in the PRC, legally you need to be working on this visa. The exception is if you are doing something classified as an internship or a fellowship, for which an F visa is usually the correct one.

Because it requires more trouble and paperwork, a bit more expense, and you would be put on the tax rolls, dodgy companies often refuse to sponsor the Z visa and want you to come in and work on some other classification. Understand that if this is the situation you are facing, YOU are the one taking the risk of technically working illegally. Magnitude of that risk depends on nature of what you will be doing, clout of the company you are working for, duration, which city/town you will be located in, etc. It does not matter that you were born in China, etc. The fact is you hold a foreign passport. I suspect that whoever is hiring you feels pretty safe that as native-born (and I presume fluent Mandarin speaker, reader and writer), you will "pass" for local so will slide under radar. This will likely be true, but what I said before still goes as far as legality and risk. There are some "pluses" to working illegally and not being on a Z: easier to avoid income taxes, easier to change employers as on a Z, you need a formal release letter from Employer A before you can get work permit transferred to Employer B. These are, admittedly, quite attractive reasons for avoiding being legal.

D visas were originally intended more for older retired Chinese living abroad, with different citizenship, who wished to return to PRC for good. D's don't allow work privileges, and at any rate have become sort of an anachronism and replaced by other paperwork/procedures. Not an option for you. Ex-PRC citizens with relatives can get a one-year L visa with no restrictions on duration of stay or entries/exits. However, it does not come with work privileges. Occasionally 2 years are granted but there are no recent reports of success on the long length coming out of the USA. There is a new residency permit (which is what you're really after) process just announced in the last couple of months, and it is aimed at Chinese with other citizenships, who want to come back but who want to keep their current citizenships from another country. I don't know a lot of details on it or whether it eases the way for legally working. There was a recent thread on this on this forum, but not very in-depth. So, Google industriously and you can find out more about this. Many are reporting that the Chinese Embassys abroad, and their websites, are not exactly clear and useful references on this new development, but you can inquire.

As for regaining Chinese citizenship, I'm sure you could. But understand that the Chinese do not allow dual citizenship for adults, so they would certainly insist you renounce your US citizenship. (The USA allows duals so that isn't an issue.) This would give you Chinese residence and work privileges, but you would then be needing visas to visit the US and many other places. And I have no idea how you would get a new hukou permit in China that gives you official identity as resident of a specific city. This would be a big step with potentially life-changing repercussions, not to be taken without thinking through all the angles.

Hong Kong has completely separate immigration and visa issues from the PRC, but for working there, you do need the proper visa and cannot do so on the standard visa-less entry (which I think is time-limited for US passport holders anyway).