Solved

Driver training does not always work

What did you try to do?
I trained my driver on "All" attributes, only Stamina is maxed out

What happened instead?
The progress bar filled over to the next level but no attributes increased

Did the problem happen while using wi-fi, mobile data, or both?
Both

Did the bug happen in the app, on PC, or both?
Both

What is the model of your device?
Redmi note 8 pro

What is the operating system?
Android

What is the version number of the operating system?
Android 11 RP1A.200720.011
MIUI 12.5.7.0

What operating system is your PC?
Windows 11 Pro 24h2

Which browser did you experience the problem in?
Chrome

Can the bug be reproduced?
It doesn't always happen, I'd say about half of the time. I had this issue both when training All or only Driving Ability / Mental and when using different amounts of training (1x or 10x), on all platforms. I also tried to reset cache to no avail.

Additional comments:
video proof https://www.youtube.com/watch?v=C9lDhtUbp4o
I managed to level up again after the video and it said "+2 Defending", but it only increased by 1 (went from 16 to 17) https://imgur.com/a/eTmHMPS

Yeah the training is quite buggy. 
Maybe it’s taking a while to update the stats? Because I have issues with the stars. I train my drivers and pit crew and first it shows 4.5 stars and when logging in after a few hours suddenly I have 5 stars. Then I train again and the stars become red, even though I didn’t reach 100 and no stats have increased.
It’s definitely something to look at.

The video was recorded on the windows app, version 5.000 (573). I was not aware there was a newer version, I'll definitely try updating it (I thought updates were automatic or that at least the app would notify me if there was a new version).

The issue appeared on chrome too, even after clearing the cache with the CTRL+SHIFT+DEL shortcut. I'll try this way too.

Thank you for the reply.

I play on iphone and I try to clean the cache regularly. It doesn’t happen all the time. I noticed that often the game doesn’t refresh on its own (for example when buying a new staff member or driver you have to hard close the game and reopen it in order to actually get it). So maybe that’s what I’m experiencing with the stars. 

Ok, now I paid really close attention to it and the problem I am facing is the game doesn’t refresh on its own.
I trained a driver, he had 4.5 stars. The training bar reached 100% and a stat was improved but still 4.5 stars were shown. I cleared the cache and then my driver was shown with 5 stars.
So seems to be a refresh problem. Would be nice if that could be fixed, because it’s pretty annoying :)
I don’t know if this might be also the cause of Barney’s issues.