Welcome to the forum!
My best guess is that you may have mistakenly used a Shape option, on the control bar of the Pen/Bezier tool, when you drew the path. That automatically applies an LPE (live path effect) which can have unexpected results like you have described. (In this situation, the path effect can be used to create a variable width path. But there are many other different kinds of LPEs, which are not used with with this tool.)
If you'd like to share your SVG file with us, we can confirm. Or you can confirm it for yourself by selecting the path with the Selection tool (before you use Stroke to Path), and looking at the status bar. When the Selection tool is enabled, the status bar tells you what kind of object is selected.
Edit
If it's a path effect, you can remove it by Path menu > Remove path effects. If the status bar tells you something else, please tell us what it says, and we can tell you what to do. Or if you'd rather share the SVG file, that's fine too
