There are ST19 movements with power reserves. Here are most of the Seagull ST19 movements. If it's their BB homage that comes in pink, it has the ST1905.

ST1901	2 register	small seconds at 9	30 min counter at 3
ST1902	3 register	small seconds at 9	30 min counter at 3	12 h register at 6 that mirrors the time-keeping hour hand
ST1903	3 register	small seconds at 9	30 min counter at 3	24 h register at 6 that is not affiliated with the chronograph function
ST1905	2 register	small seconds at 9	30 min counter at 3	decentral power reserve at 4
ST1906	2 register	small seconds at 9	30 min counter at 3	decentral power reserve at 6
ST1907	2 register	small seconds at 9	30 min counter at 3	central power reserve indicator
ST1908	4 register	small seconds at 9	30 min counter at 3	date at 12
ST1940	2 register	small seconds at 9	30 min counter at 3	automatic

 

Thanks for this - extremely helpful. Seems the ST1905 has been around since at least 2007, but I can't many watches that use it. Odd

 

... Any idea what specific movement this could be?

i suspect that both the ST1905, ST1906 & ST1907 may share several parts 🤔
on this video, the top plate of the ST1906 has already holes for rubis (+ extra work) that could be used for the ST1905 or ST1907 (or possibly both)

Hoping one day, they will provide the full technical documentation, i try to collect what i could here ...
if someone has something, do not hesitate to share or send 🙏