Nvh264enc pipelines no longer working in GStreamer 1.26

Pipelines including nvh264enc, which worked for me fine in GStreamer 1.24, are no longer working in 1.26. Not sure if nvh264enc broke in 1.26, or if there are changes requiring me to amend my pipelines. I’d welcome any help.

Example pipeline that worked in 1.24 but fails in 1.26:
gst-launch-1.0 -v videotestsrc ! videoconvert ! nvh264enc ! rtspclientsink location=rtsp://127.0.0.1:8554/test

1.26 failure message:

Use Windows high-resolution clock, precision: 1 ms
Setting pipeline to PAUSED ...
Got context from element 'nvh264enc0': gst.cuda.context=context, gst.cuda.context=(GstCudaContext)"\(GstCudaContext\)\ cudacontext1", cuda-device-id=(uint)0;
Progress: (open) Opening Stream
Pipeline is PREROLLED ...
Prerolled, waiting for progress to finish...
Progress: (connect) Connecting to rtsp://127.0.0.1:8554/test
ERROR: from element /GstPipeline:pipeline0/GstNvH264Enc:nvh264enc0: Could not encode stream.
Additional debug info:
../sys/nvcodec/gstnvencoder.cpp(1251): gst_nv_encoder_init_session (): /GstPipeline:pipeline0/GstNvH264Enc:nvh264enc0:
Failed to set format
/GstPipeline:pipeline0/GstVideoTestSrc:videotestsrc0.GstPad:src: caps = video/x-raw, width=(int)320, height=(int)240, format=(string)NV12, interlace-mode=(string)progressive, framerate=(fraction)30/1, multiview-mode=(string)mono, pixel-aspect-ratio=(fraction)1/1
ERROR: pipeline doesn't want to preroll.

Please report this as an issue in gitlab, together with a full debug log. Thanks!