Soft Start Inrush Current Limiter- PCB design

[Muzzer]

The issue is actually about the transformer cores periodically saturating when connected to the mains, something that happens on a fairly random basis as I explained. The tendency for them to saturate depends on how much magnetising flux has been designed in and how close that is to the saturation flux limit.

Some transformers run very close to saturation and are more prone to the effect than others. To increase the margin requires higher inductance which in turn requires more steel and copper and higher material cost. There's a commercial decision involved, which is one reason we see variation between different examples.

You may notice that apparently similar transformers from different suppliers behave differently - this may be seen as different steady state (unloaded) temperatures, for instance. I'm guessing your toroidal audio transformer doesn't run a high magnetising current / flux, which is why you don't see tripping breakers. I have 2 yellow site transformers that are both rated at 3000VA and are of similar dimensions, yet one sits at around 50C and the other barely warms up (perhaps 30C) when left powered but unloaded.