Single glyph suddenly incompatible

Out of a sudden one glyph became incompatible. I can figure out the affected master but no reason: shape order, node order, anchors, all those parameters are fine. It happened after a failed mouse click.
Do you have an idea what could be wrong in this case?

Now I found it by myself after staring at the vectors for hours.
In another master than expected an initial node somehow moved to a handle.

You can troubleshoot these kinds of things by using View > Show Master Compatibility. If you select a node, it will display the corresponding node in the other master(s) and you can thus see where the error arises. Tip: use Tab to step through all nodes of the path.

Thanks, SCarewe!