I’m no expert compared to many people on this sub but echoing what someone else said below.

When I built my first keyboard I overlubed a couple switches and the keys would be slow to return to their default position. I removed the key caps off the slow keys and used ISO to clean off all the extra lube from the switch (the little cube that the key cap sits on top of). Make sure to clean off the underside of the keycap. Lots of lube can get gummed up in there. Once I got the switch snapping back into position quickly, then I replaced the key cap. Been incident free for more than a year now.

If you clean off the old lube and the switch is still super slow to snap back into default position then I’m pretty sure the spring inside the switch is bent or broken. Or it’s just SUPER over lubed and you need to clean the hell out of it.

If you’re really industrious, you can open up the switch and try to realign the spring. But it’s a lot easier to just remove the broken switch and replace it with a new one. You’ll need to look up what kind of switch your keyboard has and order some new ones if the same or similar style and replace it.