Can't add collaborator - error 500 when submitting the form

Describe the issue or problem
I’m trying to add a collaborator to an article that already has an author, but the form won’t submit. Checking the browser console, I see a 500 error response.

What application are you using?
For example, OJS 3.2.0.3 (yes, very old!)

Additional information
The URL that is called by the form submit is: DOMAIN/FOLDER/index.php/methaodos/$$$call$$$/grid/users/author/author-grid/update-author?authorId=

It doesn’t have any variables, that seems wrong. Checking the PHP error_log, I see this:

PHP Notice: unserialize(): Error at offset 0 of 27 bytes in /home/USER/public_html/FOLDER/lib/pkp/classes/db/DAO.inc.php on line 357

PHP Fatal error: Uncaught Error: Call to a member function getData() on null in /home/USER/public_html/FOLDER/plugins/generic/ror/RORPlugin.php:88

Stack trace:
#0 /home/USER/public_html/FOLDER/plugins/generic/ror/RORPlugin.php(75): RORPlugin->getCurrentAuthorAffiliation(NULL, ‘en_US’)
#1 /home/USER/public_html/FOLDER/lib/pkp/classes/plugins/HookRegistry.inc.php(107): RORPlugin->handleAuthorFormExecute(‘authorform::exe…’, Array)
#2 /home/USER/public_html/FOLDER/lib/pkp/classes/form/Form.inc.php(314): HookRegistry::call(‘authorform::exe…’, Array)
#3 /home/USER/public_html/FOLDER/lib/pkp/controllers/grid/users/author/form/PKPAuthorForm.inc.php(205): Form->execute()
#4 /home/USER/public_html/FOLDER/lib/pkp/controllers/grid/users/author/AuthorGridHandler.inc.php(331): PKPAuthorForm->execute()
#5 /home/USER/public_html/FOLDER/lib/pkp/classes/core/PKPRouter.inc.php(391): AuthorGridHandler->updateAuthor(Array, Object(Request)) in /home/methaodo/public_html/revista-methaodos/plugins/generic/ror/RORPlugin.php on line 88

For future reference, deactivating the ROR plugin fixes it. I’m waiting till the next LTS version to upgrade my whole install and get rid of these problems.