I recently accepted a summer job (internship) Employers have been asking for i-9 documents and I have been postponing it waiting for a notice from USCIS.

Monday is my official start date. I have to show my current EAD and explain that reregistration is still under process.

Has anyone been in a similar situation

well need to wait to see what the federal register says about filing TPS and automatic EAD renewal for exipiring TPS EAD.

first the notice has to be published in public inspection and only will be final to be published in next day or two's official notice so keep checking the federalregister.gov
it typically updates 7:45 AM, 11:15 AM and 4:45 PM EST everyday .

i think, they can't deny you the internship due to future expiration date . see the below:
https://www.uscis.gov/i-9-central/i-9-central-questions-answers/faq/what-do-i-do-when-employees-employment-authorization-expires
NOTE: You cannot refuse to accept a document because it has a future expiration date. You must accept any document (from List A or List C) listed on Form I-9 that on its face reasonably appears to be genuine and to relate to the person presenting it. To do otherwise could be an unfair immigration-related employment practice in violation of the anti-discrimination provision of the INA.