Updated Ubuntu Mate on RPi 4 8GB. It rebooted and ran. Subsequent boots fail with messages:
Initramfs unpacking failed: Invalid magic at start of compressed archive
spi=bcm 2835 fc204000.spi could not get clock -517
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Sign up to join this communitySimilar errors have gotten a variety of responses. None of which applied here. So I burned a fresh image of Mate on a micro SD card and it now works. Thanks, JPB