when turning on a plug-in like comp

[bluesfordan]

is it normal for the volume to make a substantial jump? Is it just over-enthusiastic default setting?

[Farview]

is it normal for the volume to make a substantial jump? Is it just over-enthusiastic default setting?

Yes. Especially if it has a low threshold and auto makeup gain.

[witzendoz]

Probably the input gain is turned up and the threshold and ratio are not set up properly. As Farview suggested, is the auto makeup gain turned on? I often set the input, and ratio then turn the makeup gain on or off depending on what I am looking for in what the compressor is going to do in the mix.

Alan.

[keith.rogers]

Yup, look for auto-gain settings in the compressor.

Logic Pro X defaults to both Auto Gain (at -12dB) and Auto release. Your compressor plugin might be similar. (In Logic Pro X you just have to turn it off and then Save As Default to stop it from doing this. You may have that option in your DAW/plugin.)

[mixsit]

is it normal for the volume to make a substantial jump? Is it just over-enthusiastic default setting?

I dislike the behavior and zero it out on my plugs and templates. For one they almost always over do it (gee wonder why? To give them bit of 'hype maybe..?)
If a bit of make-up is needed with lots of reduction, fine dial it in. But most of the time you're knocking off mostly peaks. That does't well represent -loudness-

[GONZO-X]

you should approach every plug as if you are using an external device,
and realize it's your job, to match up levels,
whether it's input or output.

if you don't realize that you've doubled your output, for example,
and do not understand why,
you need to back up,
and take a new look at the basics of recording.