Patents in China are filed first, and the patents filed first are valid. What you said may happen, but it should be noted that the patentee generally needs to submit the patent evaluation report of the utility model to the court when claiming rights, because the utility model has not been examined, which is equivalent to the examination of the utility model, and the examiner will find this problem, leading to the failure of the claim.
2. Patents are regional. Patents filed in the United States can only be protected in the United States, and patents filed in China can only be protected in China. In other words, if someone else applied for a patent in Japan, but not in China, then they can use this technology at will in China, as long as it is not exported to Japan.