H1B visa transfer to another employer when the current I94 is just valid for another month only

Hi, I'm a full time employee of my current employer A and my H1B visa and I94 is valid till 02/21/2020 only. My current employer A is still in processing of filing the extension with USCIS and its not yet filed.

Now, I got a full time employment offer from another big consulting company B and they have already filed the H1B amendment case too in normal processing, expecting the case Receipt# to be received in next few days.

I'm curious of knowing the issues I can face on joining B on receipt notice before expiring on my I94 i.e. joining them before 21st Feb itself. I understand the risk of RFE and finally rejection of amendment case of employer B on joining on receipt. And in that case, I need to immediately leave US. Is there any other glitch I can face.

Thanks & Regards