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Refer to optifine download page for compatible versions of optifine and forge (including optifine preview versions)

The error is something to do with a time out when accessing a file to check its md5 checksum. There is very little context to the error other than it is during your "processResources" Maybe you have a file locked in your src/main/resources or something like that? Try restarting your ide. Using --stacktrace or --debug when running the build from the command line might give more information about what it is doing?

https://forums.minecraftforge.net/topic/117477-119-how-to-access-blockentity-data-from-containerscreen/ for sending data and accessing block entity data in a container menu/screen for the client. It is not done by default as it would be useless work if it wasn't used. You can only use DataSlots for integers. e.g. the furnace does this for burn/cook time progress and duration, or the lectern does it for the page number. This only sends the data to the client if you open a container so it is more efficient, but less flexible. See those vanilla examples for how to do it. e.g. look at how LecternBlockEntity.dataAccess and LecternMenu.lecternData are used.