I have gotten a quality condenser up to epic quality, and have not gotten any more module slots, any idea what is going on?

you get more slots to upgrade items with, aka more inventory size, not module slots.

The wording on the mod description indicates otherwise. The plural use of module(s) was misleading.

I'm guessing getting extra module slots with higher quality levels got changed at some point, and the dev forgot to update the description.

For now, the best you can do is change the Module slots number to 5/6 in Mod settings>Startup>Quality condenser, and operate on the honor system for putting modules in the condenser.

Edit The misleading line in the description I believe is this.
"Higher qualities of the machine itself are faster and have more upgrade slots,
note that beyond 100% quality there is no bonus, so you could use speed modules then."

nah this mod has always been like this, everyone seems to confuse slots for items to upgrade with module slots.

Hmm ok. Guess I was wrong about that fact in the first part of my post.

The second part of my post still applies though. Because yeah, when saying upgrade slots, most English speaking people I know would think it meant/was a synonym for module slots. If you actually meant item slots, you should probably reword that sentence to say something like

"Higher qualities of the machine itself are faster and have more [Inventory/Item] slots
note that beyond 100% quality there is no bonus, so you could use speed modules [in spare/excess slots] then"

Just my 2 cents anyway shrugs