Never.

At least it never has for me, and I’m probably old enough to be your grandfather.

I’ve tried everything - desensitizing toothpastes/mouthwash (though I wouldn’t expect those to help with flossing pain), salt water rinses, every type/brand of floss.

So yea, don’t believe everything medical professionals tell you about how things “should” happen. The operative word there is “should”. As in “usually”, or “most often”.

Everyone is different, so not everything will work the same for everyone. (I can go through a laundry list of meds that work/don’t work/negative side effects/no side effects for individuals in my family. The variability is astounding among a group of genetically similar people).

Best you can do is be consistent with your flossing, find the right type for you (I find the waxed tape style the best for me), brush at least 2x/day (preferably 4x), use the right brush style (generally as soft as will work) and I found using a modern electric toothbrush helps tremendously (especially the Phillips Sonicare, they have some actual studies behind their efficacy). After going through a few different toothbrushes, the Philips is so effective for me that my annual cleanings have gone from sucking to being a breeze.