I don't believe the Youtube error message is saying it WON'T upload the clip (unless you are finding that it actually won't proceed!), but that the settings aren't optimal for the type of video you are uploading.
Interestingly, comparing the Premiere 'Youtube 480p SD' preset, the only anomaly I can see is the bitrate, which Youtube recommends at 2.5mbps (where the frame rate is 24, 25 or 30fps), or 4mbps (where the frame rate is 48, 50, or 60fps). The preset is currently set to 8mbps, so it might be worth trying to reduce this to match the YouTube recommendations.
YouTube compression algorithm is very complex. As SamLanes said in the comments the preset 'Youtube 480p SD' you’re using might have a higher bitrate than the recommended. You could try to use a plugin like AfterCodecs to make sure you always have the optimal settings for Youtube: https://www.autokroma.com/AfterCodecs
But you can do a lot more with AfterCodecs, it’s a very useful plugin for PP, AE and AME. It gives you all the codecs you might need - like ProRes 422 / 4444 / XQ, all 4 HAP codecs and many more - in .MP4 and .MOV containers. It also gives you the best and fastest compression for H264 / H265 with a lot of customization like the ability to render in 8K, FileSize targeting, custom Framerate, custom Resolutions and youTube profiles. Plus it has some cool features like MultiRender Markers to batch export clips in PP and the ability to export all Audio tracks separately.