my "game cash on start" is now resolved.
Process experienced and recovery
1. Install upgrade fails (due network disconnection or failure to access mod web point).
2. After re-install retry (many times). pack finally fully installs.
3. try to play ==> game immediately fails to start (and some times mine craft launcher does not activate)
4. I delete the mod pack including all backups of the mod pack (purge the mod pack, loose worlds unless side wise copied)
5. Install mod pack (usually after many install attempts)
6. try to play game and is usually works. if not
7. if game fails to start go back to 4 and repeat.
8. if game still fails to start remove all mod packs, twitch, and delete the curse install directory entirely.
9 reinstall everything again, and it can take more than 24 hours to effect a successful install.
NO MODIFICATIONS have ever been applied to the minecraft suite of programs, twitch or mod packs.
Multiple reboots of machine required, and during this times windoze updates for windows 10 have been applied multiple times... these unstoppable updates definitely interfere with the mod pack installs using twitch.
In my professional opinion after 30 years as a IT programmer, designer and analyst is that a much more robust installation process is required that does not roll back the patch in the current manner. a better solution is to apply the update to a new profile and allow the update to complete in that profile by making the update process to detect the install fail and restart the install process and reapply the missing elements of the mod pack. I have experienced dual element installs when updates have failed and this directly caused by the update process not actually checking what is installed and making the correct installation decision, which may require replacing the elements already installed. There should be no need to re-download the mod pack file, and I do not understand why it is necessary to visit source points for every mod on the web when they are already in the mod pack that is down loaded.
Having wasted days resolving these installation problems I am less than impressed with the poor installation design and wonder if there is the attitude "that it is better to drink soft drinks through a straw stuffed up a nostril rather than through the mouth" in the mind of some software designer...