Drainpipe slime --- do I need to care?

Depends on what the bar soap is wrapped in!

I find the idea strange that solid soap, once dissolved in water & rinsed down the drain with more warm water, is going to precipitate in the pipes.

I use 60°C or higher about once a week, but I wash most outer clothes at low temperatures because they last longer that way.

A bit of slime (not much) appeared again a couple of days ago; from the way it's positioned I'm almost certain it's come from the bathroom hopper (so nothing to do with laundry). I've run some sodium hydroxide through the shower drain.

This house is too old for separate drains.

I'll just turn the grid so the slots are parallel to the outlet I think it's coming from.