Very interesting question.
Thanks for providing all the dates, that is very helpful.
When you say "trustee" are you referring to the Chapter 13 trustee or the Chapter 7 trustee? I'm going to presume you mean the Chapter 7 trustee.
Also, I of course defer to whatever your personal bankruptcy
lawyer is telling you. I presume you are just looking for more helpful input.
The primary question is "when" was the April severance pay "earned." Or in other words, was there any thing that could have happened where you would not have received the April payments. For example, if you had gotten a job on March 27, would you still be entitled to the April payments. If so, the Trustee has a decent argument that the pay was not postpetition earnings, but rather merely a receivable existing on the date of conversion.
If however, you would have lost the funds if you had gotten a job on the conversion date, then arguably the receivable had not yet vested and was therefore not an asset of you (and the estate) as of the conversion date.
That is my reaction.
Let me know if I'm missing the point of your question!