WiFi drops after several days

[David Melgar]

Raspberry Pi 3b+
OS version: Linux octopi 4.14.94-v7+ #1193 SMP Tue Jan 22 15:34:30 GMT 2019 armv7l GNU/Linux

PRETTY_NAME="Raspbian GNU/Linux 9 (stretch)"
NAME="Raspbian GNU/Linux"
VERSION_ID="9"
VERSION="9 (stretch)"

This system had been running rock solid recently. >60 days without a reboot. Decided to upgrade to latest Stretch. Updated firmware, updated OS. All updates applied.

After several days of operation, WiFI failed. This has happened twice. Pi still seemed operational running OctoPrint server, printing to 3d printer. Pi is headless. Print continued but unable to ssh. Pi won't respond to ping.

Looking in /var/syslog the following messages appear at the onset of the error:

Jan 30 19:18:45 octopi kernel: [328749.038717] mmc1: Timeout waiting for hardware interrupt.
Jan 30 19:18:45 octopi kernel: [328749.038839] brcmfmac: brcmf_sdiod_sglist_rw: CMD53 sg block write failed -110
Jan 30 19:18:45 octopi kernel: [328749.038851] brcmfmac: brcmf_sdio_txfail: sdio error, abort command and terminate frame
Jan 30 19:18:55 octopi kernel: [328759.278771] mmc1: Timeout waiting for hardware interrupt.
Jan 30 19:18:55 octopi kernel: [328759.279017] brcmfmac: brcmf_sdiod_sglist_rw: CMD53 sg block write failed -110
Jan 30 19:18:55 octopi kernel: [328759.279029] brcmfmac: brcmf_sdio_txfail: sdio error, abort command and terminate frame
Jan 30 19:18:55 octopi kernel: [328759.279926] brcmfmac: brcmf_sdio_hdparse: HW header checksum error
Jan 30 19:18:55 octopi kernel: [328759.279937] brcmfmac: brcmf_sdio_rxfail: terminate frame
Jan 30 19:19:17 octopi kernel: [328781.519181] brcmfmac: brcmf_do_escan: error (-110)
Jan 30 19:19:17 octopi kernel: [328781.519196] brcmfmac: brcmf_cfg80211_scan: scan error (-110)

Error repeats from there.