On all of my realms (in creative and survival) when you use an anvil on an item, the item is renamed to '#' signs. There will be as many # signs as there are characters in the original name (including spaces) and this happens whether you are editing the name or not (for instance this happens if you are intentionally renaming something or if you are combining weapons/items/applying books). This does not happen in a non-realms creative or survival world - including in an exact downloaded copy of the realms world. 

Steps to reproduce:

Create a Bedrock realm (Survival or creative)

Obtain an Item, an Anvil, and any enchanted book

Use the Anvil to apply the enchanted book to the item OR attempt to rename Item in anvil 

View final product.

Expected result:

The items name will remain unchanged and the enchanted book will be applied OR the items name will be renamed to the name the player created

Observed Result:

The characters (including spaces) in the Items name will be replaced with # symbols 

ex. 'Bow' will become ### or 'Netherite Boots' will become '###############' 

Again this only occurs in a realm setting - to test you can download a copy of your realm to your device as a single player world and repeat the above steps; the issue will not occur in a single player setting.