Part of the TF2 Community Fix-Up Pack: https://steamcommunity.com/workshop/filedetails/?id=2156577890

The class selection HUD element suffers the following issues:
1) The lighting on the models is awkward due to a removed spotlight
2) All animation sounds, such as the ground impact sound when the soldier slams the rocketlauncher on the floor, do not play at all
3) The facial animations don't get reset when the class model changes
4) The class animations are jittery, skip frames or have delayed playback

Issue #1:
The class selection screen in the years dating from 2007-201x had a spotlight to boost the appearance of the playermodels.
When the code for the playermodels on the HUD was being updated around the time of Mann Vs Machine, a spotlight that shines on the playermodels was removed.
This likely was done unintentionally. This results in dark, contrasted lighting which doesn't look great, especially on the character faces.
The fix for this is adding the spotlight back into the .res file for the class selection HUD, restoring the old lighting.
However, after discussion with several TF2 community creators, the lighting was adjusted to be a middleground between the old and current lighting.
The old lighting was too bright, and the current lighting is too harsh, the middleground gives a sweet spot between the two.

Issue #2:
Similarily to above, the class selection screen featured sounds that played during the class animations.
Example: a click sound when the Medic locks his feet, or a chamber twirl sound when Demoman spins it.
Around the time of Mann Vs Machine, these sounds suddenly stopped playing.
After researching the code and comparing between 2007 TF2 code and 2016 code, this feature was lost when the playermodel code was being updated to a new shared system.
The fix involves integrating code into the playermodel system that allows the sounds to play again.

Issue #3:
In the class selection screen, when changing between class models, the facial animations will not get reset instantly, and instead slowly decay themselves over a second
This results in awkward facial expressions such as the mouthes being wide open for a second.
The fix simply changes this "decay" to be instantenous instead of taking some time.

Issue #4:
Around the time of Gun Mettle update, the class selection animations starting experiencing poor playback, e.g. being delayed, skipping half of the frames or having jitter issues.
Investigating the 2016 code, I was able to fix it. However, this fix did not work on the latest build of TF2.
After spending time reverse engineering the client, it turns out the code for the playermodel HUD element was changed slightly during Jungle Inferno.
By patching the client.dll bytes to skip a certain function, the animations worked flawlessly. However, this broke the Loadout screen, making the character be stuck in an A-pose.
Since I have found the root cause of the issue, I provided information about what I gathered, and hopefully Valve will be able to get a proper fix working on their end.

Special thanks to rabscottle for the thumbnail and video.
Note: the proposed lighting in the thumbnail and video is no longer accurate, I have updated the submission with a new middleground after discussion with several TF2 community creators.