The latest official version of it is 4.2, and can be found
here.
The lock/unlock is most likely caused by something else that also alters the same things. I'd say go through your plugins and see if something else does something similar and if so, disable that.
The gag is a known issue and there's no real fix for it. If you search for it on this board you should be able to find a relatively bad solution for it posted by me, though (it's in a thread with someone else having that issue).
The reason amx_speed not working is probably also because of a conflict with another plugin. This plugin may alter the maxspeed values every now and then and this causes the amx_speed not to work.