That will be hard to help on this one, as we don’t do fixes of older Babylon versions.
Have you tried with 5.0? I know we fixed some “It is undefined behaviour to use a uniform buffer that is too small” warnings, but I don’t remember if it applies to spotlights or not…
Note also that if you get this warning only a single time (or a small number of times - meaning, the number of logs in the console log does not rise infinitely - or at least does not reach 250, which is I think the limit after which the browser stops logging an error), it is ok, it means the problem is only transient and your program is fine.