As the title says, I get a RLG error every time this does seemingly happen, and it has happened to me twice.
This makes the sieges rather unplayable and is a rather frustrating and game-breaking bug that makes me avoid them altogether.
I do not have an extensive crash log or even the details of the RLG (sorry about that Produno, reporting this belatedly) but i think it is sure to happen to anyone reaching that stage, as I saw that I am not the only one.
I should point out that at the time of the crash my battle size was 750 or so. (Possibly I reduced it to 500 as on occasion battles get laggy on that size, especially in sieges)
PC Specs: Sapphire Radeon RX 480 4GB
AMD i5-6402p 2.80GHZ
8 GB ram