Recent versions of KiCad (>=8?) have started creating Gerber files that have RS-274X extensions %TA% %TD% %TF% %TO%.
When loaded by gerbv, the rendering is still perfectly fine, but it fills the console and the Messages pane with complaints like

Unknown RS-274X extension found %TF% at line 3 in file "/redacted/test1.gbr"

I found a pretty small example that I attach here: zest-Edge_Cuts.txt

The only mention of this issue I could find online was in an out-of-the-way place:
X2 extensions should be ignored, by react66, Aug 23, 2021
alyoshin/gerbv-dxf-builded#1
Note the date: over four years ago! Maybe this issue will be better at reaching the right people.
In that issue, react66 included the helpful comment:

Gerber X2 has adds four new commands (TF, TA, TO and TD) to attach attributes to a Gerber file. All pre-existing commands remain unchanged.

I can confirm the effect on the Debian-shipped gerbv versions 2.9.6 and 2.10.0.
I haven't yet built gerbv from github source to find out if it silently got improved.