FIrst of all, when testing remove Optifine, as that only add more stuff to the log which isn't really necessary (also sometimes Optifine can be the cause of some issues itself..)..could you share your modlist, complete with the version of each mod?
I believe, someone correct if I am wrong, but Pixelmon was taken down by the request of Nintendo themselves. And that the mod should not be distributed.
when i click install on the Pixelmon modpack it gets to 42% and mod 3 out of 7 and then gives me the error message:
Timeout attempting to download:
"https://edge.forgecdn.net/files/3072/298/pixelmon-1.12.2-8.1.2-universal.jar"
when i posted this i only got a response saying
"1.12 is no longer supported on this forum.
Please update to a modern version of Minecraft to receive support."
and the comments were closed after that so i could not ask any questions. This was not helpful at all.
responding to what they said though: i had just downloaded minecraft yesterday on this new pc, and i have the "latest release" as one of the installations.