Macros in email template(s) getting corrupted

Where and how are you adding the macros? This sounds to me like the WYSIWYG editor is trying to fix the markup - the issue should be between the quotes and single apostrophes. I would maybe try using apostrophes in the first example for href attribute:
href='{% GetResourceString("dd.newsletter.footer.linkedin.url") #%}'

And for the other macros, I would maybe try using open condition statements:
{%if (GetResourceString("dd.hcemail.footer.facebook.url") == "pending client") { %} style='display:none' {%} else {""}%}

Hey Juraj,

The macros are added inside of an email template editor. Thank you on your advice. I have changed everything as per your instruction. It's important to note that the macros work for a while, so I don't think that the WYSIWYG editor has anything to do with this at all. The macros stop working later at a seemingly random time.

The macros have broken in the same way again. Using the "open condition statements" didn't remove the cause of the issue..

It's now turned into this

<a href='{% GetResourceString("strings.facebook.url") #%}' target="_blank" rel="noopener noreferrer" data-auth="NotApplicable" {%="" if="" (getresourcestring("strings.facebook.url")="=" "pending="" client")="" {="" #%}="" style='display:none' {%}="" else="" {""}|(identity)globaladministrator%}="">

Basically, these things ="" are being randomly added after everything inside of a macro and are destroying all functionality.

This is really strange. What happened in the mean-time? Are you using staging, web farms, export/import, etc.? What other changes were made you can think of? Are you using always the same browser? If yes, are there any plugins/addons? I would maybe try using some other browser or disable the plugins for some time to see if they are interacting somehow.
Also, are the corrupted values also saved into the DB in the CMS_EmailTemplate table? If yes, then there is something which is saving the corrupted data - any custom code or integration in place? Even if it sounds unrelated...

I can't answer you Juraj because I don't have the technical know-how, I will answer as soon as I know.