You're right, autoptimize_filter_js_exclude cannot remove items from dontmove, only from the items added in AO's "exclude from JS optimization"-settings (I'll have to look into that, there's something to be said for having the filter be able to change all exclusion-strings).
Some possible short-term solutions:
* set "force JS into head"
* add "SlimStatParams" to the exclusion-list
Alternatively you could just change the dontmove-array in classes/autoptimizeScripts.php, removing wp-slimstat.min.js from it.
Having done a small test, I can confirm wp-slimstat.min.js does not need to be excluded for it to work. It is entirely possible that users who had slimstat break after autoptimization were actually having some other JS being broken, halting execution of the autoptimized JS alltogether, with slimstat as the victim, not the reason.
Conclusion; we might have excluded wp-slimstat.min.js too soon (but there are solutions for those who need them). Camu: what's your take on this?
frank