oh, you're using welding?
than everything can happen : - )
on a more serious tone:
welding is not a (yet) a stable feature.
if you're encountering issues, and you really need the welding, you're welcome to experiment with simpler documents and see what is really happening. once you have a minimal example that can be reproduced, please fill a ticket with attached the document and with the steps to reproduce the bug.
the address for the bugs is:
https://bugs.scribus.netwithout being able to see the document, there is not much more that i can do for you. sorry.