Hit something similar a fair time ago, and installed havenged¹ to stop it repeating. Less necessary now as the kernel has its own similar (jitter based) internal entropy source, and /dev/random has been made non-blocking anyway by adding a little extra compute to “stir the pot” (like /dev/urandom did anyway, but less cryptographically safely so).

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[1] https://manpages.debian.org/bookworm/haveged/haveged.8.en.ht...