I have found lots of post, from many a mod about this error. So I think it might be something else reacting to your mod.
I was playing around in a single player world, I made a few simple IC gates, I thought 'gee, this is amazing'. When I made my first serious IC gate and place it, instant crash, with that dreaded packet error. I can't return to the map undo this.
If there is a limit to what the ICs can hold, perhaps a 'piece limit' on them would help sort this for others. But I rather hope you folks have a fix, tbh. I was only trying to make a driver for your 7 segment display. I didn't think it was that big a circuit. But seeing that the simple IC gates didn't suffer from this makes me think it may be a size issue. Here it is. ... I didn't think '2x7seg' was a killing word.

Thank you in advance for any help.

Where is the crash log?

This must be related to NBT on the ItemStack. There isn't much we can do about it, but i have some thoughts i need to ponder over for a bit.

Has this been fixed already without closing this issue?

This IC that I created yesterday appears to be larger than the one in #1316 (closed as duplicate of this) but my game does not crash when placing it. It stops/lags for a few seconds, but then it works fine.

@covers1624, can you look over this one last time before we close this out? My understanding is that PacketCustom handles splitting large packets.

No longer relevant. Fabrication is receiving a major rewrite in the 1.15 port