Game version is 1.3.47m - Public, on Microsoft's Xbox Game Pass.
I am currently playing a custom campaign (stored in UserContent/Campaigns) with no additional mods, and I've noticed that my Court Mage Wizard's Spell Shield power is no longer granting temp HP. The character is a High Elf Wizard, Court Mage subclass, Level 7.
I can still use the power, and it recovers correctly on long rest. When used, the dialogue box says "X activates the SPELL SHIELD power", but it is missing the two follow-up "X now has Y temporary hit point(s)" lines. The character portrait shows a "Temporary HP" buff, but the HP number does not have the +X showing any temporary HP. Dealing damage to myself confirms there is no temp HP, and the "Temporary HP" buff goes away too.
There seems to have been some sequence of events that lead to the ability to stop working, but the exact moment it stopped working is beyond my auto-save history now. If I create a new Court Mage at my current level (Lv 7) and start a new campaign, the power works correctly and grants +35 temp HP as expected.
Lastly, it doesn't seem to be a bug with temp HP, because if I drink a Potion of Heroism (+10 temp HP), the character gains +10 temp HP as expected.
Based on another Reddit comment, I am not the only one who's run into this: