I found they released their "new" game "Kingdom Rush Vengeance" which was released 14 months ago on Steam here yesterday. So I think it's necessary to talk about this studio.

1. I bought one of their games "Kingdom Rush Frontiers" on GOG years ago.

2. They released one update on January 9, 2020 on Steam.
https://steamcommunity.com/app/458710/discussions/0/1743389952524783916/

3. I found the GOG version was still outdated on November 2020. I contacted GOG support and asked the devs on Steam forum myself.
https://www.gog.com/forum/general/games_that_treat_gog_customers_as_second_class_citizens_v2/post2015

4. More than one month later, they finally updated the GOG version.

5. This year, they released another big update on September 1 on Steam.
https://steamcommunity.com/app/458710/eventcomments/3039354735042916564?snr=1_2108_9__2107

6. Again, until now, GOG version is outdated.
And this time they even successfully released another game here yesterday.
https://www.gog.com/forum/general/release_kingdom_rush_vengeance_9f77c

How could this happen? How can the devs and even GOG treat their customers like this?

Well, I can't stand unwinnable endless-type levels (even though I like "losing is fun" games like Space Station 13, go figure) and microtransactions, so that missing update would get a "good riddance!" from me. Not a good thing that a game's missing features, but I can't bring myself to care about that particular update.
At least Vengeance is here, more than three years since it was released elsewhere.
And it just got a Chinese-themed update apparently, wonder if it's included or it'd take another three years to see it here. Does anyone know?