Designers

Can't figure out what's going wrong with my designers. Last season (my debut), I invested heavily in design, got them leveled up quickly, and assigned ten per part. I put the slider to "next season" and I was quickly at 100% for "next season". However, this season, with the same settings, I'm only getting one percent every couple of weeks from them. Is there something I'm missing?

Yes,
If you commit too much to design to a seasons parts and reach 100%  it will have a knock on affect the following season where your design will be hit.

Extract from beginners guide:
"Focusing a lot on one season has the downside that the design team won’t be able to improve much on the other season parts anymore. Therefore, the continuous challenge is to keep a good balance between this year’s and next year’s performance"
So you need to find a compromise.

its basically wat happened to the Ferrari F1 team last year and this year but vice versa

New players need to be advised to read the beginner's guide and the rules of the game, and also search the forums for topics that may have already been discussed...questions like these keep showing up way too often when it could easily be resolved by reading the two most important manuals in the game!

In  Rules & Regulations, Technical, paragraph 2.1 Car Design :

"Next season gains are based on current season performance levels
When a team focuses a lot of energy on one season it has a negative impact on the next. This prevents a team from ever becoming unstoppable."

Sorry, I thought that line in the beginner's guide referred to adjusting the slider. Is there a certain next-season percentage at which I need to divert resources to the current season to avoid throttling?

so to to clear up if i have a design of average say 60% on my parts, and my next season is 50% does that mean my design for next season is 50% of this season (meaning 30%) or do i start at 50%?

you start at the % developed. (meaning 50% design completed for next season).