The overstay fine when the new visa is being processed

I've done signing and thumbmark, then when they submit the papers to the MoL, it told them that they need authentication of the diploma. They gave me another paper from MoL to sign and make a thumbmark again.

Well! In that case, you may be charged an overstay fine of AED100 per day.

You can request your new employer to pay it for you since the process was delayed by them.

Ask the PRO of the company to be sure.

I am on a leave as of now. After the signing and thumbmark, what is the next process, and how long is the process for the visa?

Please check with the PRO of your new company.