Could this be a bug? I opened a circle to create an arc with a thick stroke. I then used Object > Pattern. The stroke immediately changed to thinner. This didn't happen when converting other shapes, including a full circle. I tried various arcs, both closed and open. This happened with all except a full ellipse/circle. I'm on Windows 10 64-bit.

This doesn't happen if I group the arc or convert it to a path.

I noticed a similar issue last week when converting pattern to object.  I could not get a repeatable process.

I cannot reproduce the issue with the ellipse/arc. Win, Inkscape 1.1.1.

Please share an Inkscape svg file.

I've included the closed arc with thick stroke, duplicated it, and used Objects > Pattern.

The behavior of patterns on a path seems to have changed. It now ignores the styles of the pattern source and traces only the geometry along the target path. You must then apply your preferred style to the target. Speaking for myself, I prefer this new behaviour. 

Why is the left arc a slice object? It shrinks its stoke width but used as a pattern shows the former width here.

Are patterns on a path relevant to the Pattern function, Paddy? After something's converted to a pattern, you can't change the style.  One can convert the arc to a path first, and that still seems to work with the style retained, but I was noting an anomaly with arcs that isn't there with other shapes. I just think it feels buggy.

Polygon, I was showing the original shape I drew on the left. Unlike what happens with other shapes, the arc doesn't retain its stroke width for me.

The one on the left is labeled "Slice".

Try the following: generate a new file and first make a new layer - now draw your arch (Here´it´s labeled "chord" for whatever reason) - when done go Objects->Pattern->Objects to Pattern. No shrinking of the stroke width:

ok... looks like my 'ol buddy "user-units" is gone off the reservation... 

The issue does not occur when the document properties scale is proportional to 1px : scale=1. (mm would have scale 3.77953, in would have scale 96)

It is very curious that it does not occur with a circle.

Please report this as a bug and link to this conversation.

While the other shapes and paths seem to behave properly in @hildybingen's file, when creating another object and filling with the same pattern, the pattern will be absurdly large.

Bug report exists here: https://gitlab.com/inkscape/inkscape/-/issues/1636

Re: #6 above. Sorry hildybingen. I completely misinterpreted the question. I jumped feet first into the wrong conversation.

Thanks Tyler!  Glad I don't have to write a bug report! 😅

Paddy, no problem.