There's a pretty major bug in V20 Experimental 6 where aliens have unlimited grenades, are able to throw them through walls, and use them at every available opportunity. We've spent the day trying to fix it, but we've not had any success so far so we've just rolled back to V20 Experimental 5 so people can play that over the weekend if they want.
V20 Experimental 6 will hopefully return on Monday, but we're currently unsure. It's actually quite a complex issue and the grenade spam was a symptom rather than the actual disease.
In short, there's an issue in the accuracy code where the AI is not being fed the correct "to hit" information for its shots. This is why they would always use grenades, as it thinks it is unable to hit the enemy with normal weapons - but it also means that if we remove their grenades, they won't attack the player at all. Therefore we can't hotfix it like we planned yesterday.
We don't know when this bug will be fixed, nor if it will reveal further bugs when it is fixed - so we'll just carry on working on it and let you guys know when Experimental 6 is ready to be released again.