I'm unsure whether or not this is a problem on their end or here.

I'm using the latest version (3.0.11.) 1.15.2.

In the overworld, I can place hanging fairy lights normally, but in the Tropics dimension from the Tropicraft mod, whenever I click to place hanging lights it acts like I'm placing a new line. So I click once to start hanging, but the second starts another line, a third click starts another etc etc. I end up with a whole line of hanging lights following me and I cannot remove them unless I break the starting points.

This happens with all types of lights, creative and survival.

Let me know if a log is needed for this issue, but here's an image;

Fairy Lights 3.0.12 is now out to resolve this issue.

Thanks for reporting!

I've reproduced the issue and it appears this occurs in all dimensions other than overworld. A fix will be under way.