Wpa_supplicant log says drop_unicast_in_l2_multicast: Read-only file system

My wpa_supplicant.log file says that

Failed to open /proc/sys/net/ipv4/conf/wlp0s20f3/drop_unicast_in_l2_multicast: Read-only file system
Failed to set IPv4 unicast in multicast filter

What can be the problem?

ProtectKernelTunables=true in wpa_supplicant.service. You may want to open bug report.

Thanks. What problems this could cause? I does not seem to be normal operation.

I have opened a bug report: Bug 1208610 - Wpa_supplicant logs drop_unicast_in_l2_multicast: Read-only file system