More questions on MEP to SEP

Scenario #1

MEP adopter terminates services with MEP effective 1/1/2020.  Per agreement, once termination occurs, they immediately are no longer eligible to contribute to MEP.  New plan is not effective until 5/1/2020. It is established as a new plan with a short plan year in the document.

Can the employer withhold contributions from 1/1/-5/1/2020?  I am assuming no since there was not a "plan" in place.

If the answer is no, if the employer withheld contributions, what should the ER do with them?

Since there is a gap in the time from leaving the MEP to the new SEP, how does this impact testing?  Would HCE determination be from 5/1/18-4/30/20?  What about prorating the compensation limit?  For top heavy, would the 12/31/20 balance be used for 20 &21?

Scenario #2 

MEP adopter leaves the plan effective 4/30/2020, New Plan is established 5/1/2020.  Document indicates it is a short plan year for the first year.  How does impact testing? HCE determination.

Do we test contributions from 1/1-4/30 under the MEP and only test contributions from 5/1/2020 through 12/31/20? 

Scenario 1 --

Where did the withheld contributions go? If they did not go into trust, you might be better off with an approach that involves there being no plan between 1-1 and 4-30.