@Mykle1
Today, I tried the following:

MM 2.1.2 + Electron 1.7.5 --> CPU 100% during transitions

MM 2.1.2 + Electron 1.4.15 --> problem still there, CPU 100% during transitions

MM 2.1.0 + Electron 1.7.5 --> problem still there, CPU 100% during transitions

MM 2.1.0 + Electron 1.4.15 --> problem (probably) gone, CPU 40% during transitions

So i guess you have to downgrade both, MM and electron…!?