I started a new game, 1850 campaign as Austria, on a fresh, unaltered install, with the Patch_PON_1.04July17.exe installed over it.
In the second round, my !HostLog.txt tells me:
[...]
18:39:16 (Reporting) Sardinia-Piedmont Checking if Ruler on Position: 0 should be replaced
18:39:16 (Reporting) Sardinia-Piedmont Vittorio Emanuele II di Savoia lives another turn
18:39:16 (Reporting) Sardinia-Piedmont Checking if Ruler on Position: 1 should be replaced
18:39:16 (Reporting) Sardinia-Piedmont Massimo d'Azeglio lives another turn
That's how it should be, I guess. But then the plague starts. The first to die is Abdulmecid of Turkey:
18:39:16 (Reporting) Ottoman Empire Checking if Ruler on Position: 0 should be replaced
18:39:16 (Reporting) Ottoman Empire Abdulmecid I lives another turn
18:39:16 [Warning ] Ottoman Empire Position 1 is EMPTY!:
18:39:16 (Reporting) Ottoman Empire New RulerItem Vacant assigned to this faction on position: 1
18:39:16 (Reporting) Ottoman Empire Checking if Ruler on Position: 1 should be replaced
18:39:16 (Reporting) Ottoman Empire Vacant lives another turn
The Chinese Emperor steps with him into the grave, and many others follow the example:
18:39:16 (Reporting) China Checking if Ruler on Position: 0 should be replaced
18:39:16 (Reporting) China Xianfeng lives another turn
18:39:16 [Warning ] China Position 1 is EMPTY!:
18:39:16 (Reporting) China New RulerItem Vacant assigned to this faction on position: 1
18:39:16 (Reporting) China Checking if Ruler on Position: 1 should be replaced
18:39:16 (Reporting) China Vacant lives another turn
18:39:16 (Reporting) Baden Checking if Ruler on Position: 0 should be replaced
18:39:16 (Reporting) Baden Leopold I lives another turn
18:39:16 [Warning ] Baden Position 1 is EMPTY!:
18:39:16 (Reporting) Baden New RulerItem Vacant assigned to this faction on position: 1
18:39:16 (Reporting) Baden Checking if Ruler on Position: 1 should be replaced
18:39:16 (Reporting) Baden Vacant lives another turn
[...]
This pattern is followed by - it seems - all other states in this round. Suddenly all of them die and are replaced by "Vacant".
PS. I started the game again, same install, but with my Austrian colonisation capabilities added, and exactly the same rulers died again between the second and the third turn.