Hi there! This is something i thought could be a reason, just my 2 cents of opinion,
The films that you used are films that
absorbed alot of heat, so when compared to just glass windows, the window with film will be hotter.
Heat is a form of energy, so it can either be
absorbed, reflected or transmitted through.
In this case for your windows with no film, it absorbed abit of heat (glass itself absorbs heat) but allowed most of the heat to transmit through.
For the window with film, it absorbed more heat into it (both glass and film absorbs heat), but allowed lesser heat to transmit through.
The infrared thermometer you are using is measuring the temperature at the glass area / on the glass, thus you will see higher temperatures for the window with film.
To truly test the effect of the films, you should be testing the ambient or room temperature of the room, and not the window temperature. For this, you need 2 side by side rooms (1 with film, 1 without) to truly test the effects.
One thing to note is, most films technology in blocking heat is through absorption, so heat will not pass through the glass, and just get trapped in the film/glass. However over time, as the heat builds up in the glass and film, the heat will slowly dissipate into the room as secondary radiation.
If you want better heat rejection films, you can consider sputtered films with silver that can reflect heat, thus the performance will be stable and consistent. A true high performing sputtered films are ones that can truly reflect heat WHILE maintaining clarity (not mirror like effect). There are types that are sputtered films but are highly reflective like a mirror, and most still just absorbs heat.
Hope this is useful!