Using Google Sheets I'm trying to populate a list of countries with (among others) names, ISO-alfa2 code, and flags. I use this IMAGE() and ArrayFormula() to get the flags from URL in my private server:

=ARRAYFORMULA( IMAGE(URL/"&P7:P224&".png")) Where URL is the link hosting the flags, RANGE P7:P222 contains ISO 3166-1 alpha-2 codes (all in upper case). The flags in the URL labeled with the same ISO codes except with lower case.

As shown in the attached picture, some flags randomly don't show up despite that all ISO codes have been entered the same way (all upper case) and all the flags images are lower case.

Things I tried:

When using LOWER(P7:P222), some flags don't show up. When using UPPER(P7:P222) some different flags don't show up. I used both Chrome and Firefox to view and edit the sheet.

Is there a way to fix this without changing the range to lower case or the images name to upper case? Is it something wrong with my formula or is it just the browser, HTTP/GET or Google app is misbehaving? Any input is greatly appreciated!