/dev/rtc missing on Ubuntu core 18

I have Intel Denvetron based device on which /dev/rtc and rtc0 are missing.
Error that I see at boot up -

[ 12.041110] rtc_cmos 00:02: RTC can wake from S4
[ 12.098168] rtc_cmos: probe of 00:02 failed with error -16

I have following configs in my kernel.

CONFIG_RTC_LIB=y
CONFIG_RTC_MC146818_LIB=y
CONFIG_RTC_CLASS=y
CONFIG_RTC_SYSTOHC=y
CONFIG_RTC_NVMEM=y
CONFIG_RTC_INTF_SYSFS=y
CONFIG_RTC_INTF_PROC=y
CONFIG_RTC_INTF_DEV=y
CONFIG_RTC_I2C_AND_SPI=y
CONFIG_RTC_DRV_CMOS=y

Could not see any existing topic in forum on this.

Is this a custom kernel? Does it work with reference pc-kernel ?

Apologies for delayed reponse @mborzecki. Was on leave.
Yes, its a custom kernel. I did found a fix (disabling watchdog related config). But have run into a reboot issue for which I have raised - Wdog reboot after config change