Newsletter does not send – Stuck at Adding Subscribers to Queue

Problem:
When attempting to send a newsletter, the plugin “sits/hangs” at the message “Adding Subscribers to Queue” and never moves past this point.

“Test this email” under Newsletter -> Edit works every time.

Settings -> “Test Email” works every time.

Troubleshooting:
I have changed back to the default WP theme with no change.
Uninstalled and reinstalled the plugin with no change.
Ran the template reset options under Settings -> Advanced with no change.
Tried a different template with no change.

I am testing out the free version before I purchase, however right out of the gate I have run into this problem. Any assistance would be greatly appreciated for a prospective buyer.

The issue I am running into sounds similar to support topics below which are both unresolved:

https://www.ads-software.com/support/topic/not-sending-8/
https://www.ads-software.com/support/topic/sends-the-test-mail-but-not-the-newsletter/

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My Debug Info:
WordPress Version: 4.8.3
SendPress Version: 1.8.11.5
PHP Version: 7.1.10
PHP Memory Limit: 256 MByte
PHP Memory Used: 33.65 MByte
MySQL Version: 5.5.5

Send Setup: SendPress_Sender_Website

Database Tables:
wp_sendpress_subscribers_tracker OK
wp_sendpress_subscribers_url OK
wp_sendpress_url OK
wp_sendpress_subscribers_status OK
wp_sendpress_subscribers OK
wp_sendpress_list_subscribers OK
wp_sendpress_queue OK

———-
My Support Info:
// Generated by the SendPress Plugin //

Multisite: No

SITE_URL: https://centralregion2.dcf.state.fl.us/mis
HOME_URL: https://centralregion2.dcf.state.fl.us/mis

WordPress Version: 4.8.3
Permalink Structure:
Active Theme: Suffice 1.0.10

Registered Post Stati: publish, future, draft, pending, private, trash, auto-draft, inherit, archive, sp-standard, sp-custom, sp-form, sp-autoresponder, sp-systememail

Platform: Windows
Browser Name: Chrome
Browser Version: 62.0.3202.75
User Agent String: Mozilla/5.0 (Windows NT 10.0; Wi
n64; x64) AppleWebKit/537.36 (KH
TML, like Gecko) Chrome/62.0.320
2.75 Safari/537.36

SP Version: 1.8.11.5

PHP Version: 7.1.10
Host: DBH: localhost, SRV: centralregion2.dcf.state.fl.us
MySQL Version: 5.5.5
Web Server Info: Apache/2.4.28 (Win32) OpenSSL/1.0.2l PHP/7.1.10

WordPress Memory Limit: 40MB
PHP Safe Mode: No
PHP Memory Limit: 256M
PHP Upload Max Size: 2000M
PHP Post Max Size: 30M
PHP Upload Max Filesize: 2000M
PHP Time Limit: 90
PHP Max Input Vars: 1000
PHP Arg Separator: &
PHP Allow URL File Open: Yes
WP_DEBUG: Disabled

WP Table Prefix: Length: 3 Status: Acceptable

Show On Front: posts
Page On Front: About (#2)
Page For Posts: (#0)

WP Remote Post: wp_remote_post() works

Session: Enabled
Session Name: PHPSESSID
Cookie Path: /
Save Path: C:\xampp\tmp
Use Cookies: On
Use Only Cookies: Off

DISPLAY ERRORS: N/A
FSOCKOPEN: Your server supports fsockopen.
cURL: Your server supports cURL.
SOAP Client: Your server has the SOAP Client enabled.
SUHOSIN: Your server does not have SUHOSIN installed.

ACTIVE PLUGINS:

Active Directory Integration: 1.1.8
Active Directory Thumbnails: 1.06
Archived Post Status: 0.3.7
Awesome Changelog: 1.0.1
Better Notifications for WordPress: 1.6.7
Changelogger: 1.3.1
Co-Authors Plus: 3.2.2
DLM Changelog Add-on: 1.1.1
Download Monitor: 1.9.9
Members: 2.0.2
NewStatPress: 1.2.9
Page Restrict: 2.2.8
PJW Mime Config: 1.00
SendPress Newsletters: 1.8.11.5
TinyMCE Advanced: 4.6.3
UpStream: 1.12.4
UpStream Calendar View: 1.0.0
UpStream Customizer: 1.1.4
UpStream Email Notifications: 1.1.2
UpStream Frontend Edit: 1.3.8
UpStream Project Timeline: 1.0.10
weDocs: 1.3.3
WP-Optimize: 2.1.1
WP Author Bio: 1.5.5
WP User Avatar: 2.0.8