I created my character using the "Human_Dummy_S" template, using "import PSD assets". When i go to use my character the lock buttons don't work (they work fine on the original template).

I'm having the same problem.  I used the same template, sent it to photoshop and then added my own sprite layers.
Sending the psd back to CTA 4 and the locks are now gone, There is still IK on the limbs and the locks are stsill 
there in the UI but there's no way to "unlock" them.  

Judging by the lack of answers on this thread, it could  take a while for someone to suggest a solution.

Looks like the same problem in this thread, although I'm getting it using both using import and export.:
https://forum.reallusion.com/412815/2D-Motion-Key-Editor-Locks-stop-working?Keywords=lock

Hello e1_scheer, 

Sorry for the inconvenient, if the problem still occurs, 
please send your project and screen record to our customer support if it'll be all right, 
our tech team will take a look at it.

Customer Support : https://www.reallusion.com/CustomerSupport/UserEx/QForm.html

Thank you so much for the feedback!
DanielC

Hi Daniel,

Thanks for following up on this

I restarted the character from scratch using the same CTA template
"Human Motion BoneF"  and after going back and forth using the photoshop
pipeline button it worked this time round and I can switch the IK locks on and
off.

That solves the problem for this character but I have no idea at what 
point the photoshop link broke the constraints in my previous attempt..

I'll keep an eye out and post back if I find out more.

Thanks for providing the workaround, that actually helps a lot.
I would follow this up and see if we can reproduce the issue.

DanielC