I have a HP Stream 14 laptop running Ubuntu 18.04 that also had the CMOS Reset (502) Checksum error. The way I fixed this was by using a newer kernel than that which Ubuntu 18.04 ships, specifically a version above 4.19. My Ubuntu shipped with 4.15.0-42-generic and this caused the CMOS error.
I used the mainline/upstream kernel 4.19.0-041900-generic, and sleep works without any CMOS errors. You can follow the Ubuntu wiki for instructions: https://wiki.ubuntu.com/Kernel/MainlineBuilds
Another option that worked was to use one of the kernel releases from the Linux Kernel Archives at: https://www.kernel.org/
If you go this route, the only one I tested was 4.20-rc6 (4.20.0-042000), and it worked.
To the best of my knowledge this first method of just using a newer kernel only works with kernel versions 4.19 and above.
This second method worked for me before the newer kernels fixed the CMOS on sleep error. It requires you to compile your own kernel with the fixed DSDT table. The above method works well, but for those who might need something for older kernels I did this second method.
With the 4.18.6 official release I had the CMOS error. What I did to fix the sleep on 4.18.6 was to follow the Arch wiki link below and to edit the DSDT tables using
iasl and change two of the RTC values:
0x0070, // Range Minimum
0x0070, // Range Maximum
0x00, // Alignment <-- This one was made 00
0x02, // Length <-- This one was made 02
Again, this method worked for me on the 4.18.6 kernel version, I did not test other kernel versions.
You can follow the Arch DSDT wiki: https://wiki.archlinux.org/index.php/DSDT
Make sure however that you compile it into the kernel, not by the CPIO archive method. I recommend HP Stream 14 users to simply use the first method because it saves space and time.