The slow Gibbles spawn seems pretty simple, AFAIK. They get up quickly when they spawn, and they get up slowly after they use the jump attack. If a Gibbles uses the jump attack even one time, including a failed jump attack from the wall glitch, every Gibbles that spawns from that point forward will have the slow spawn animation. It appears that the game replaces the spawn animation with the jump attack animation by mistake after any Gibbles uses the jump attack.
The only way to fix it is to close the game and open it again. (It's been suggested that dying can somehow fix the spawn animation, as well.) Unless you're able to freeze and kill every Gibbles the moment it spawns so that it never has a chance to jump, preventing the bug is pretty much impossible. Desync with the spawn animation between clients can cause situations where other people can attack the Gibbles, but you can't, most likely because you got the slow spawn, and they didn't.