Media Encoder yields blank videos with nests

Have encounted an unusual problem with Media Encoder.(version 23.5, build 51).  I cannot render a nest without a blank video-- it ignores the video aspect, and only renders audio into the output file.  But when I render the underlying clips, it's all fine.  When I render the nest directly from Premiere (version 23.5, build 56), it works fine also.  Underlying clips are h.264 and h.265.