I'd built a storage system using conveyor grabbers with specific items whitelisted, conveyors behind them and crates in front of them. However I observed a strange behaviour, where a few of the crates wouldn't get any items. I conducted a test in a creative world (screenshot below) and it confirmed that every 5 blocks along a conveyor line, the grabber's 20-tick delay would align in such a way that the item manages to pass straight by it with no interaction.

On the screenshot below, every grabber was set up with a whitelist allowing only the particular colored concrete variant placed atop it. No upgrades were used. Red scaffolds mark grabbers who didn't manage to grab their corresponding items.

One solution could be to count the delay starting from the last tick an item was grabbed, rather than ticking every nth tick, as is the case now: