So, I managed to somewhat track down the cause. There’s clearly things which have changed in the way gradle handles things between versions that impact this.
In the commit d22fb4bcce5925d29f36ba83e3c33e25055a5785 on 11/16/2020 at 3:15:33pm, the gradle version was changed on line 25 to 4.0.0 in Engine/Source/Programs/UnrealBuildTool/Platform/Android/UEDeployAndroid.cs
When building with this change in version, what gets linked into libUE4.so (and likely other aspects) is changed significantly. While it builds, it seems no testing was done for the impact on the rest of the process, as if you just go in to this file and change it back to 3.5.3 then you will get build sizes around what you had in 4.25.
I’m using a source build, but that file is in the packaged build in source form, so you should just be able to open it up and edit it to get things sorted while using 4.26 until it’s properly addressed.