Hm... any other thoughts?
By applying the butterfly net, you are making this ASB.
Any significant migration of a millions of people will have significant butterflies before 1939-1945 time window. First it will be by far the largest white settlement in Sub-Sahara Africa after South Africa. It could easily be the largest. With the hostile natives being displaced, you will have a well armed Jewish population that speaks a dialect of German (Yiddish). You will be displacing 100K's or 1,000K's of blacks if you don't just kill the blacks. There are at least two overlapping case of Genocide in this period in Africa committed by whites.
So now we start looking at butterflies from just this item.
1) Long-term the ethnic cleansing/genocide of blacks in Uganda will make Africa much more prominent in black Americans minds. It will make the Congo a widely know event. It means the USA is likely less friendly/more hostile to the UK. You will see butterflies out of this item everywhere.
2) You are depopulating the Pale of Settlement. You are making areas of Poland that are a Polish plurality a Polish majority. You are making some areas where Jews are the plurality become Polish Plurality. You have just buffed Polish nationalism. Poles normally left Poland for lack of economic opportunity. You are opening up jobs for Poles in Poland. Fewer Poles move to Germany and the USA. You might see immigration reverse so Poles are moving from Germany to Poland.
3) The Tsars were not pro-Jewish. There were Pogroms. With a big home for Jews, you might see mass involuntary deportation. This will amplify #1 and #2 greatly.
4) If we assume WW1 still manages to go about like OTL, you are creating more severe labor shortages. It can have interesting implications on the concept of blaming Jews and Lebenstraum. There is nothing better than abandoned farmland to persuade people that we have plenty of room.
5) You may invite a Colonial response by other powers. For example, do Italy or Germany feel threatened by this large population center. Do they try to encourage/force immigration to the East African possession?
6) This Jewish army is the dominant land power in East Africa. The probably fight constant war with the blacks, so probably are decent fighters at least in small unit warfare. Who do the support? Remember these are Russian Jews who speak Yiddish who the UK helped Maybe the go the true neutral route? Fighting for the Entente risk retaliation against Jews under CP control (Congress of Poland). Fighting for Central powers risk retaliation by Russia. We may be creating an Armenian like situation.
7) By gutting parts of the Pale of Settlement of Urban population, you are making the food situation better in WW1. It can have profound impacts on the war.
Ok, so handwavium you write a TL where these things are manageable. The numbers were small enough. Somehow you keep the impacts of the East African battles manageable. Germany/Russia makes enough mistakes to just make up for the benefits gained.
Now Europe falls into Chaos in 1919. Polish/Russian War. Russian Civil War. Famines in Russia. It will give you mass migration of Jews resulting in huge demographic changes to Poland/Belarus area.
1) You have to go look and decide who the Jews supported in the Poland Russian War. Who did they back in the Russian civil war. Big butterflies.
2) You are depopulating Urban areas. Some town/cities were up to 95% Jewish, are they empty now? Empty cities of 50K people change the idea of Lebenstraum.
By the mid-1920's, TTL will not look like OTL. It is just impossible.