Problem

My Sim resets/jumps when he tries to send metals for melting via the mail box

Cause

The new collection journal and the resulting changes in the collecting skill has lead to a few things breaking.

You need to collect each kind of metal the usual way (picking of the ground) to initialize the collection skill properly before you can use any other means like the cauldron or  magic to acquire the metal.

Solution

Collect each metal manually once. It has to be your sim. Giving it to someone else does not count.

Mods, that help with the issue

• Overwatch solves the issue with V73 and above

Further Reading

• Gem cutter doesn’t cut gems