a: 1: {s: 18: “custom_css_post_id”; i: -1;}
This is how WordPress core stores this value in the database for all themes, not just Exoplanet.
for example in the options table (usually ‘wp_options’ but I see yours is named ‘soa_options’ as you are using ‘soa’ as the prefix), if you look at the Twenty Seventeen or Twenty Sixteen theme mods you will see that they are the same:
SELECT * FROM soa_options WHERE option_name = 'theme_mods_twentyseventeen' OR option_name = 'theme_mods_twentysixteen'
run the above SQL query and you will see that these themes also contain a: 1: {s: 18: “custom_css_post_id”; i: -1;}
If you switch theme to Twenty Sixteen do you still see the same error?
Can you take a screenshot of your screen where you are seeing ‘exoplanet requests for the settings’ please?
You can upload images here in your posts.