[2022] Unable to Equip Syndicate Sigils on Excalibur

This issue is on our radar. Fortunately it is one that you can easily work around until we develop a true fix.  The problem is that you will not be able to put a syndicate sigil on a warframe if the same warframe/appearance is chosen in your conclave loadout.  This is because syndicate sigils are not allowed in conclave, so, when the game validates your loadout before saving, it removes what it thinks is an invalid item. Avoiding the problem is as simple as choosing a different warframe appearance than what is equipped in your conclave loadout.