2nd transfer while 1st trf in progress, what are all the risks


In 2019 my H1b transfer filed in PP by employer E1, I started working on receipt notice but denied after RFE. As I-94 was valid for few more days from date of denial, E1 quickly filed another new transfer petition for same client which gave me 240 days.

Now 140+ days passed and got an offer from employer E2 (Full time from ex-client), and they filed transfer in regular (considering the pending petn) and asked me to join after approval.

My question is, as the current project ended with client at E1 may I join with receipt notice to E2.
though E2 attorney may agree, as its hard to stay longer w/o proj with E1, I worry if any risk here.

I believe no more 240 days for this new transfer petition, what will happen in worst case.

Appreciate your valuable advices.