So it was a wire and not a check?
This is odd and, while I believe you are saying what you have been told, I don’t believe “did not inform the plan sponsor of any issues/delays” at all. The sponsor is not being upfront OR their spam filter is too tight.
Check bounced? Insufficient funds?
Or was it deposited, but perhaps with no allocation instructions, and after getting no response for how to allocate/invest, they sent a check for the trustee to transfer to another trust account for the plan to be held somewhere outside of the R/K platform?
Some other reason?
The reason it was returned may help for guiding them.