May be wrong, but I thought the user manuals for fridges tend to say “do not use with extension leads”.
Guessing really, but one reason might be that the current surge when compressor starts might overwhelm a typical extension lead, leading to momentary voltage drop at the socket outlets.
You could try replacing the extension lead with a high-end one with extra thick cables, which might help in above scenario. But my worry would be, since appliance fires are in the news nearly every day, if the manual says not to do it and a fire broke out, even if unrelated to this, what would insurers say if you’d ignored the user manual?
Emphasise again, I may be wrong, fridge manuals may not all say “do not use extensions”.