Drop down list of reviewer information not accessible in Add Reviewer

Further to this, I have reviewed the thread here https://forum.pkp.sfu.ca/t/reviewer-list-wont-load-ojs-3-0-2-0/29677 which seems to centre around a PHP Warning: json_encode(): Invalid UTF-8 sequence in argument

Our error is different - some of the reviewer’s pop_List_Panel_Item_details expand (about 1 in 10) but most just do not expand. I tried inserting the debug line
Something like this before line 162
error_log(print_r($jsonObject, true));
This served to show that jsonObject is correctly generated for both good and bad reviewers - so seem that the issue is occurring between this point and the HTML served.

Nothing else looks concerning in error_log

I have also gone into the database and trawled for odd characters, eg.
select username, email from users inner join user_interests on user_interests.user_id=users.user_id inner join controlled_vocab_entry_settings on user_interests.controlled_vocab_entry_id=controlled_vocab_entry_settings.controlled_vocab_entry_id where setting_name='interest' and setting_value like '%;%';
And deleted any interest values with punctuation characters - also this does not fix the issue

Please can someone help?