Magento 2.4 "Incorrect theme identification key" issue while creating Custom cron

I am getting "Incorrect theme identification key" while creating custom cron job. Magento version is 2.4.2.

https://i.stack.imgur.com/TENqk.png

Error in log file:

[2021-06-18 00:50:38] main.INFO: Cron Job update_qty_leatherhides is run [] [] [2021-06-18 00:50:38] main.ERROR: Cron Job update_qty_leatherhides has an error: Incorrect theme identification key. Statistics: {"sum":0,"count":1,"realmem":0,"emalloc":0,"realmem_start":208142336,"emalloc_start":197509928} [] [] [2021-06-18 00:50:38] main.CRITICAL: Incorrect theme identification key {"exception":"[object] (InvalidArgumentException(code: 0): Incorrect theme identification key at /chroot/home/a5ad8123/0e80a7b082.nxcli.net/html/vendor/magento/framework/View/Design/Theme/FlyweightFactory.php:62)"} []

Can any one help me to resolve this issue?

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