Trixyz

Found the same problem some hours ago. (Win10 platform)

A friend of mine joined my world and we were making a tunnel in the Nether. 

He had a diamond pickaxe with efficiency and I followed his steps. Sometimes I saw him walking through netherracks directly and taking damage from that, even though there was no space or just 1-block space in front. I wasn't able to go through as he did.

He said that he didn't see any obstacles, only I could see those blocks and mine them.

I have this issue in my world too, version 1.14.30, Win10 platform.

The losing chunks are not exactly the same each time I come back from Nether to OW. The invisible zone usually has an extension of about 20/30 chunks and it seems to be always between the coordinates x:50-350 and z:50-350. My friends who join this world are often affected by the same problem, maybe one or two of us can see the chunks correctly and others can't.

Sometimes returning to the Nether portal and entering the OW again can help re-loading these chunks. If it doesn't work, we have to exit the game and reconnect.

I have just created a new single-player infinite world from random seed to test this issue, with render distance 8 chunks. The problem persists in another area with different coordinates.