I had that too and saw some messages in dmesg-log "bcm2708_fb soc:fb: Failed to allocate GPU framebuffer (-22)"...
So, I only update the eeprom of my Pi4B+

Code:
tc@pCP:/mnt/mmcblk0p2/tce/optional$ pcp-rpi-eeprom-update -a
pCP rpi-eeprom package version: v1.0
*** INSTALLING EEPROM UPDATES ***

BOOTLOADER: update available
   CURRENT: Thu Sep  3 12:11:43 UTC 2020 (1599135103)
    LATEST: Thu Apr 29 16:11:25 UTC 2021 (1619712685)
   RELEASE: default (/tmp/tcloop/rpi-eeprom/lib/firmware/raspberrypi/bootloader/default)
            Use raspi-config to change the release.

  VL805_FW: Dedicated VL805 EEPROM
     VL805: up to date
   CURRENT: 000138a1
    LATEST: 000138a1
BOOTFS /mnt/mmcblk0p1
Install the extension pciutils.tcz and use this description of th piCorePlayer 7.0.0 -> https://forums.slimdevices.com/showt...rePlayer-7-0-0
and it works on piCorePlayer 8.0

And now, I've no more busybox-messages...
and my eeprom ist up to date...

Code:
BOOTLOADER: up to date
   CURRENT: Thu Apr 29 16:11:25 UTC 2021 (1619712685)
    LATEST: Thu Apr 29 16:11:25 UTC 2021 (1619712685)
   RELEASE: default (/tmp/tcloop/rpi-eeprom/lib/firmware/raspberrypi/bootloader/default)
            Use raspi-config to change the release.

  VL805_FW: Dedicated VL805 EEPROM
     VL805: up to date
   CURRENT: 000138a1
    LATEST: 000138a1