Blizzard have posted the current known issues list for patch 10.0.7, including an empty spellbook when logging in.

Known Issues (Source)

Dragonflight patch 10.0.7 is now live. Please read on for a list of known issues that we’re working on, and further information about this update.

10.0.7 KNOWN ISSUES
Updated March 21

Auction House

Viewing an item tooltip may change the sorting order.

Classes

Some players may see an empty Spellbook when logging in for the first time on their character. This issue can be resolved by changing to a different specialization (and changing back, if desired).

Paladin

Players who swap to Retribution Paladin from another specialization may have 2 points incorrectly allotted to Blessing of Freedom in the Class tree. This can be resolved by right-clicking the talent to remove the extra point.

Gameplay

Worgen and Goblin player-characters can leave their starting zones via Warlock or party summons.

When completing the Blackrock Depths Pet Battle Dungeon, no options are given from Tasha Riley to gain the title “Minion of Mayhem”.

Recruit-a-Friend

Recruits are not removed if they do not add gametime within 7 days of Recruit-a-Friend acceptance.