Imported project is done -- but can't render. Help/ideas?

Resolve Studio 19.1.4 Build 11 running on Windows 11. Surface Studio desktop PC. Diagnostic log attached.
SCENARIO / BACKGROUND
I had half-finished a project in VEGAS PRO a few years ago.. exported it as XML and imported to Resolve. Generally the import went fine (though it's inconvenient that all the audio is split into separate L/R tracks and not linked to the video)...
I finished editing the project in Resolve and am now trying to export.
PROBLEM
Whenever I render/export, I get an error from Resolve... either "Full resolution not found" or (when I try to export with the option to "use proxy media") "Full resolution or proxy not found" for a clip early in the timeline.
However -- that clip plays perfectly fine in the preview .. when I go to the source file it's clearly present and double-clicking plays fine in a media player. (the file is on internal SSD, not on a network or external drive.) I was able to render it once with proxy media a day or so ago.. but now that's also not working.
Media pool shows that the file has a 1920x1080 proxy (so OK quality level for rendering.. that's my target resolution) ... original source is AVCHD High L4.0.
Is there generally an understood reason why this would happen and is there anyting I can do to fix/workaround? (I'll keep trying to make it use proxy media.. but certainly would rather it rendered from native...)
Thx
SCENARIO / BACKGROUND
I had half-finished a project in VEGAS PRO a few years ago.. exported it as XML and imported to Resolve. Generally the import went fine (though it's inconvenient that all the audio is split into separate L/R tracks and not linked to the video)...
I finished editing the project in Resolve and am now trying to export.
PROBLEM
Whenever I render/export, I get an error from Resolve... either "Full resolution not found" or (when I try to export with the option to "use proxy media") "Full resolution or proxy not found" for a clip early in the timeline.
However -- that clip plays perfectly fine in the preview .. when I go to the source file it's clearly present and double-clicking plays fine in a media player. (the file is on internal SSD, not on a network or external drive.) I was able to render it once with proxy media a day or so ago.. but now that's also not working.
Media pool shows that the file has a 1920x1080 proxy (so OK quality level for rendering.. that's my target resolution) ... original source is AVCHD High L4.0.
Is there generally an understood reason why this would happen and is there anyting I can do to fix/workaround? (I'll keep trying to make it use proxy media.. but certainly would rather it rendered from native...)
Thx