Data not showing up in mailchimp

I have set up a Participants Database for customers that connects to Mailchimp. The customers are saving as expected in Participants Database. I am entering the data through the Add New Participant Record on the wordpress dashboard.

When I try to either “Subscribe to Mailchimp” or “Update to mail chimp” All of the email addresses wind up in Mailchimp but only some of the other data for some of the customers entered populates the mail chimp fields some of the time. With the majority of the additional fields empty. Below is from the log file with identifying data changed. Do you have any suggestions what could be wrong or how to identify what the problem could be?

data: Array
(
[email_address] => [email protected]
[status] => subscribed
[status_if_new] => subscribed
)

result: stdClass Object
(
[id] => d5fbb064787d6a3922cce38390a11559
[email_address] => [email protected]
[unique_email_id] => 8ae8ee5777
[email_type] => html
[status] => subscribed
[merge_fields] => stdClass Object
(
[FNAME] =>
[LNAME] =>
[MMERGE4] =>
[MMERGE5] =>
)

[stats] => stdClass Object
(
[avg_open_rate] => 0
[avg_click_rate] => 0
)

[ip_signup] =>
[timestamp_signup] =>
[ip_opt] => xxx.xxx.xxx.xxx
[timestamp_opt] => 2017-12-14T08:30:54+00:00
[member_rating] => 2
[last_changed] => 2017-12-14T08:30:54+00:00
[language] =>
[vip] =>
[email_client] =>
[location] => stdClass Object
(
[latitude] => 0
[longitude] => 0
[gmtoff] => 0
[dstoff] => 0
[country_code] =>
[timezone] =>
)

[list_id] => 06a4edd115
)

The merge fields are.

email:MERGE0,first_name:MERGE1,last_name:MERGE2,title:MERGE4,mailing_list:MERGE5