Single-finger touch event not working in cog 0.18.4 on Debian bookworm [wpe webkit 2.38.6]

[escherstair]

I have a Debian bookworm (stable) than runs on a NXP iMX8M-Plus, and I built cog by sources as suggested by @bertogg in issue #736. Now I have

cog --version
0.18.4 (WPE WebKit 2.38.6)

(cog:169): GLib-GObject-CRITICAL **: 20:42:30.266: g_object_unref: assertion 'G_IS_OBJECT (object)' failed

I can see web pages, I can scroll with my finger, I can use a mouse (if connected), but single-finger touch doesn't work in a reliable way. I mean, it seems to me that sometime something happens (I see some visual "effects" on the item I touch), but my touch is not handled as a touch/click. I tried both with short touch and long touch, but nothing changes. Is this a known limitation?