Ad clicks that are missing GCLID are clicks that came through ClickGUARD's tracking template with incomplete information.
These clicks likely did not come via Google in the first place! They are most likely being generated by nefarious bots or scripts.
Clicks without GCLID are not going to be shown in Google Ads and you will not be charged for them. On the other hand, ClickGUARD logs them and shows information on them because they did occur, and because there were (nefarious) intentions behind. They will be shown in ClickGUARD click reports as INVALID or IGNORED, depending on the specific case.
Learn more about GCLID here.