I think I actually just saw this issue discussed in a video for a different series, but I can't be certain it's the same issue. If it is the same issue, it's because of FTB Chunks. It's registering the Block Placer another player, and because you've claimed your chunk to chunkload it, FTB Chunks will only let you and your "team" place blocks there. Normally this should only matter on a server, keeping your base safe from griefing. As for fixing the issue, you should be able to go into the FTB Chunks settings and change it so to allow other players or to allow fake players. This would probably be the best option, to prevent the issue with other machines in the future, but there are other block placing machines that will still work (I don't know which beyond Refined Storage's Constructor, which I use for my own latex automation but which you aren't at the point to use yet). I believe the Modular Routers block placer has a setting that lets the game think it's you and not another player, but I don't even remember if that mod is in this pack. Also, your Hemp just hasn't had enough time to grow, it should work with more time. But you can speed up the growth with Rich Soil. Make Organic Compost (Farmer's Delight, I believe) and place it down and it will convert over time. It will convert faster near water and mushrooms. Rich Soil will grow crops a lot faster than normal Farmland.

You can use block placer from Engineer’s Decor.

0:50 🤣