I'm experiencing a weird issue with my WordPress. I'm around this for almost two months. Can someone please help me? Please be my life savior...

The issue:

When I publish a post with data in all fields (original and custom) everything seems ok. But after a few days (3-7 days on average), the data from my custom fields (only) disappear and I don't understand why. I already did the test of disabling all my plugins and I still have the same problem. So probably the issue is in my theme functions.php code, am I right?

Is there any kind soul that have enough time to check my code to see if there is anything that can cause this to happen, please? My functions.php code:

The custom fields that I have and where the data disappears after a few days are:

mr_magnifying_glass

mr_random_post
mr_feature_video

today_offer

site_id1
site_id2
site_id3
site_id4
site_id5
site_id6
site_id7
site_id8

mr_active_discount
mr_topdeal_discount
mr_new_discount
mr_lifetime_discount
mr_discount_des
mr_discount_Image
mr_discountbutton_url

mr_quility_des
mr_content_des

mr_month_price
mr_month_off
mr_month_lastrice
mr_month_price_2
mr_sixmonth_price
mr_sixmonth_off
mr_sixmonth_lastrice
mr_per_month3
mr_threeyear_price
mr_threeyear_off
mr_threeyear_lastrice
mr_per_month6
mr_fiveyear_price
mr_fiveyear_off
mr_fiveyear_lastrice
mr_per_month12

mr_feature1
mr_feature2
mr_feature3
mr_feature4
mr_feature5
mr_feature6

catag
domaintag
post_external_link
joink_external_link
titletag

discount-extra-site[]

I don't know if this helps...

Please help me, I don't know what else to do...

Thank you, guys!