Workaround steps for star tome freezing Warcraft Rumble:
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Do not claim Star tome.
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In the upper left, tap your player icon.
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Tap the Settings tab.
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Scroll down and tap “Recover Account”.
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After game relaunches, follow prompts to log into your Battle.net account.
Prerequisite: know your Battle.net username and password. (You might also need to have Blizzard Authenticator preconfigured if you’re logging in from a new location.)
This is stupidly annoying, but I can verify that it works.