Several of our process models in development have been corrupted: text boxes are

Has a CDT been changed recently? and the model is somewhere referencing an old version (signified with ^#). Trying running impact analysis on your CDTs.
I mention this because I have seen the connectors change under this scenario. Hope this helps!

It seems this environment is pointing to an invalid CDT. It's invalid now because you deleted it and uploaded again but with a different namespace:

2014-01-29 15:20:34,850 [http--0.0.0.0-8080-4] ERROR com.appiancorp.process.design.service.ProcessDesignServiceXmlImpl - An error occurred retrieving the model from the filesystem.
com.appiancorp.suiteapi.common.exceptions.AppianException: Invalid Type: null (APNX-1-4047-000)

To solve the issue:

1. DO NOT save and publish the "broken" model, otherwise you will be saving the wrong position of the connectors, the missing swim lanes and annotations.

2. Identify the problematic CDTs. Focus on the ones you recently changed the namespace

3. Reupload the CDT with the OLD namespace (you can leave the new one since it has a different namespace)

4. Open the model again. If you DID NOT save and publish the "broken" version and you reuploaded the right CDTs then the issue should be resolved. Otherwise if you DID SAVE the broken appearance the position will be the same but there will be no error in the logs any more.

5. At this point you can now manually remap the nodes to point to the namespace-renamed CDT, fix the position and missing items and save and publish

Christine, Eduardo- I believe we changed a CDT recently. Thanks for the suggestion i will try it this morning. Thanks for the prompt reply.

That was it! A CDT name was changed and the old CDT was deleted too early. We did not know this so a lesson was learned! thanks again.