Oh, also forgot to mention, have also observed problems with schottky's with larger reverse leakage currents, the BAT48Zfilm works where these other diodes don't, haven't had time to nail down precisely why yet as the alternates had a lower voltage drop, only other difference was larger reverse leakage current.

Hi,

I'm using a 3v3 only variant of this circuit but that should not be a factor.

Noticed a lot of issues with (some) modules (on some board designs) not entering or randomly not entering programming mode to various degrees. After some prodding I ended up increasing the size of the 100nF cap to 10uf and all problems disappeared over all the modules I'm using. Seems that startup timing can change between modules. My reference schematic here : https://www.dropbox.com/s/2b2c7zq3yp67ouu/Screenshot from 2019-01-13 16-52-00.png?dl=0
HTH
Fd