Thank you! I was able to fix this.
(It was somehow related to Java Script text transformers, maybe you configured one previously and BTT mistakenly didn't correctly update the action after you removed it again). This should now be resolved in 3.756!
Funny that you mention Javascript Transformation, because for me it calls my JavaScript Transformation on the clipboard item, even though I want to paste as one line.
This is my configuration, QR Code is my JS Transformation, which I use from the clipboard manager but dont want here, yet it is called when I use the shortcut.
I have this problem in version 4.566. I'm trying to use Java Script Transformer but it doesn't paste anything. Tested that the transformer works with Example input/Result and I'm using Paste items at positions: 1 as you suggested.
I've tested with simple CMD+V which also has same issues.
Copy selected text, F4 opens Alfred or Monarch and then pastes the text. What I found is sometimes text gets pasted after delay of few seconds but most times paste never happened or it took longer and I never waited. Manually triggering CMD+V works.
Used the text selection preset then duplicated the Copy action to add additional keyboard shortcut.
While cmd+v should work on all versions, the custom paste action has been completely reworked in the latest builds (5.178). Also that one can only be used if you are using BetterTouchTool's clipboard manager.