Hello @aaron1728,
I have updated the plugin to version 2.4.1 where i have fixed arrow display issue in widget testimonial design-4.
I have also checked the shortcode that you are using and i have tested the same:
[sp_testimonials design="design-2" display_quotes="false"]
[sp_testimonials design="design-4" per_row="1" display_quotes="false"]
[sp_testimonials_slider]
screenshot : https://prntscr.com/ovxt2c
Output screenshot : https://prntscr.com/ovxtbe (shortcode-1)
https://prntscr.com/ovxtk7 (shortcode-2)
https://prntscr.com/ovxtq3 (shortcode-3)
Output of widget with design-4 : https://prntscr.com/ovxu5n
Its request to add the testimonial images inside the “Featured Image” box (right bottom side during adding a testimonial) https://prntscr.com/ovxuit
Please let me know if you need more info ??