Repot it in a leaner and faster draining soil mix......or plant in the ground. The soil mix in the container - what I can see of it - looks very peaty and more moisture retentive than what lavender would prefer. A cactus/succulent or gritty mix soil blend would be much better.

They need very little water - only enough to keep them going. And no fertilizer. Lavender has a very low nutrient need and at most, a very small amount of slow release fertilizer applied in early spring will suffice for months. And may not even be an annual requirement.

it is planted in. a cactus/succulent mix....maybe too much moisture at certain times (rainy days)...

You want a soil mix with NO peat. Bark fines, granite grit, very coarse sand, Turface or perlite/pumice all OK. Whatever the current mix is, it is far too darkly colored (too much peat) to be a good cactus mix.