Should be fixed on lavender 1.0.1, if user didn't have a preference set in localStorage it was defaulting to fluid width whereas the template was starting with fixed width.
https://github.com/NodeBB/nodebb-theme-lavender/commit/339e43e715b9056b4cbb206963dd069bf9aec434
0 barisusakli committed to NodeBB/nodebb-theme-lavender default to fixed width if not set in local storage