Adding a SIP trunk causes SIP extensions to fail


This is my first post - I can usually find the answers I need in the forum but…

I have a number of SIP extensions (Linksys SPA 9**). I also have a PSTN trunk.

I have recently signed up with a couple of different SIP trunk providers. However, when I add a SIP trunk in FreePBX it causes some or all of the SIP extensions to get knocked out. It seems that my SIP phones struggle to register reliably when there is a SIP trunk present.

Has anyone else come accross this. Please let me know if you have any suggestions.