Filesystem in KVM-QEMU VM switching to read-only mode although smartctl is not reporting any errors

I have a Debian 10 Host running a Debian 10 virtual machine with QEMU / KVM. In the past few days, I got the "Error: Read-only file system" twice, after the virtual machine was running some intensive tasks for multiple hours.

I rebooted the virtual machine each time. It was telling me at boot that a manual fsck is required. I used the command

fsck -yf /dev/sda1

to fix the problem.

It worked each time, still, I want to find out what the issue is and to prevent it in the future.

I used gsmartcontrol to perform an extended check on the main drive (on the host). No errors were reported. I also used sudo smartctl -data -A /dev/sda, which reported:

smartctl 6.6 2017-11-05 r4594 [x86_64-linux-5.10.0-0.bpo.9-amd64] (local build)
Copyright (C) 2002-17, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF READ SMART DATA SECTION ===
SMART Attributes Data Structure revision number: 1
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   100   100   010    Pre-fail  Always       -       0
  9 Power_On_Hours          0x0032   096   096   000    Old_age   Always       -       19026
 12 Power_Cycle_Count       0x0032   099   099   000    Old_age   Always       -       238
177 Wear_Leveling_Count     0x0013   091   091   000    Pre-fail  Always       -       126
179 Used_Rsvd_Blk_Cnt_Tot   0x0013   100   100   010    Pre-fail  Always       -       0
181 Program_Fail_Cnt_Total  0x0032   100   100   010    Old_age   Always       -       0
182 Erase_Fail_Count_Total  0x0032   100   100   010    Old_age   Always       -       0
183 Runtime_Bad_Block       0x0013   100   100   010    Pre-fail  Always       -       0
187 Reported_Uncorrect      0x0032   100   100   000    Old_age   Always       -       0
190 Airflow_Temperature_Cel 0x0032   058   037   000    Old_age   Always       -       42
195 Hardware_ECC_Recovered  0x001a   200   200   000    Old_age   Always       -       0
199 UDMA_CRC_Error_Count    0x003e   099   099   000    Old_age   Always       -       1
235 Unknown_Attribute       0x0012   099   099   000    Old_age   Always       -       88
241 Total_LBAs_Written      0x0032   099   099   000    Old_age   Always       -       76536051093

which looks ok to me, wear still being above 90%. So it doesn't look like a hardware issue to me. What else can it be that makes my disk to keep failing?

My VM also has an LVM partition mounted via 9p, connected via the Default: Mapped driver in KVM. However, the VM is located on the main host drive. I also tried to write a new file to the mounted LVM partition after the read-only filesystem error occurred, which worked without an error. So I also don't think this partition is related to the error, to be honest.

Any idea what it could be?