This is most likely an exposure issue, not the lab trying to "fix" your photos. If a night frame is severely underexposed, the negative or scan may be brightened during printing/scanning so you get something visible instead of a nearly black image. That brightening can make the image look foggy, washed out, or oddly bright.

With film, night exposures also need extra care because of reciprocity failure (Schwarzschild effect). For longer exposures—often around 1 second or more—film does not respond linearly to light, so the metered exposure may not be enough. Different films need different compensation.

To avoid this:

• Expose more carefully for low light.
• Check whether your shutter times are long enough for the scene.
• For long exposures, look up your film’s reciprocity-failure compensation in the manufacturer’s data sheet and add the recommended extra exposure.

So the likely cause is underexposure combined with the lab/scanner lifting the image, not a development mistake.