interview cancelled by uscis

[vic2268]

Hello everyone,
I just received int the mail letter from USCIS stating this:
This is to advice you that, due to unforeseen circumstances, we have canceled previously scheduled interview on.... Monday, March 4th, 2019.... for the above applicant. We regret any inconvenience that may cause. You will be notified of any futher action taken on this case, including any rescheduled interview information, under separate notice.
So here is the thing: me and my wife went thru the interview. No decision was made on that day of the interview. On March 29, same month green card came in the mail. So now my question is?: She left the conutry 6 days before this notice, and I am about to go where she is. IS her green card not valid? can she enter the states? what is going on? is this a glitch in the system? Does anyone expreience the same situation? I am in atlanta office.
Thanks in advance,

[Enub4]

Must be a glitch. If the GC arrived then it is valid. From what I read, is very rare that they issue GC by mistake or with errors, and every time that happen, they contact the GC holder and explain the problem (about the GC) and never about the interview.

Does the letter show a date? Was it dated before March 4th or just a week or two ago?