USCIS now interprets the 24-month STEM OPT extension rule from 2016 to require a STEM OPT worker to be placed only at a worksite of the employer. In other words, the USCIS now says that any offsite placement, including at a third-party worksite, is prohibited. Will this affect the H1B petitions filed by employers for such opt students, where they are working at an end client location (not employer location) and the H1B petition was filed with end client details.
First of all to say that USCIS has changed its regulations and they do not allow off-site placements of STEM OPT extensions students is incorrect, because USCIS has said this from a very long time that they are not going to allow these placements. If you are in a situation, what can happen is you could be considered to be out of status for no fault of your own. So if you file an H-1B and if the government says well we think you're out of status hopefully that's all they can do, they can make you go outside the USA for a visa stamping.