Cross Server Friend Error

Date & Time: Most recent: 28th Febuary 2018 9:30pm GMT
Frequency: Constant
World name: Phoenix
Character name: Malin Kanji
Retainer name: -
NPC name: -
Monster name: -
Class/Level: 70 DRG
Party or solo: Party and Solo
In-game time: -
Area and coordinates: -
Housing: -
Steps:
1. Recieved a cross server friend invite from a friend (Durand Sunsteel - Cerberus Server) about a few days after 4.21.
2. Noticed next day friend was listed as (Unable To Retrieve) but had the online symbol beside the name whenever the character in question was online. Durand said the list was fine on their end.
3. Removed player from friends list around 27th Febuary 8pm GMT
4. Tried to re-add Durnad from my side 2 minutes after removing them. Red popup text on my screen, something along the lines of 'Unable to execute command'.
5. Waited 2 more hours before trying again but was met with same error message. Character in question is not on my blacklist and we tried both while inside the same cross server party and outside cross server party.
6. This is what shows on Durand's side while trying to add through Contacts: https://media.discordapp.net/attachm...=463&height=85
7. Durand has also tried adding the player listed in the image around the same time, but is greeted with the same option menu. Blue Thunder from Odin Server has however been on my friends list for over 4months now.
8. I added other cross server friends (from Cerberus) on the same days I tried to add Durand. All went through fine except Durand's.

System specs are a little difficult to specify as we're all over the place.

Malin Kanji - PS4
Durand Sunsteel - PC
Blue Thunder - PC

All of us from various areas of Europe and therefore different internet providers. Can try to supply the information if needed.