Created attachment 160517 [details]
Sequence loaded to Clip Monitor will show like this (the black bar):

SUMMARY

Bug: Sequence's Audio Waveform is not generate.

STEPS TO REPRODUCE
1. Add any clip with audio stream to timeline.
2. Create new sequence "Project > Add Sequence...".
3. Add the sequence that a clip with audio stream was added to new recent create sequence.

OBSERVED RESULT
Audio Waveform will not be generate to sequence added in Timeline, even if "Reload Clip" is perfomed in Project Bin.

EXPECTED RESULT
Audio Waveform should to be generate to sequence when added to other Sequence (Timeline) or loaded to "Clip Monitor".

SOFTWARE/OS VERSIONS
Windows: Windows 10 Version 2009 (x86_64)
KDE Frameworks Version: 5.107.0
Qt Version: 5.15.9 (built against 5.15.9)

ADDITIONAL INFORMATION
Audio Waveform also show in "Clip Monitor" when the "Always show audio thumbnails" is on (right click inside of "Clip Monitor").