If the system setting in Linnworks is set to use millimetres for dimensions, then the data sent up to eBay should convert this into centimetres as that is what the channel expects.
As it stands a 160mm long product will be declared as 160cm on the channel and therefore eBay will automatically exclude the item from it's Click & Collect program for being too long.
So currently any Linnworks account who uses mm for dimensions is most likely going to be losing out on sales because they cannot effectively offer Click & Collect on eBay.
@Andy Taylor OP did you find a workaround for this as I am experiencing the same problem, and it is also drastically increasing my global shipping program shipping rates (By 100+ euros) per item
Yes, Linnworks released a fixed middle of this year, you need to set the dimensions to "centimetres" inside the shipping part of any configurator you use for the channel.