Hello there 
Recently decided to upgrade from 2x8 G.Skill Trident F4-3200C16-8GTZR to 2 more thus 4x8. I used to run the two modules with AXMP profile turned on at 3200MHz without any issue.
Some specs:
CPU: AMD Ryzen 7 2700X
MB: MSI 450 Tomahawk max
4XDIMMS: G.Skill Trident F4-3200C16-8GTZR
ISSUE: So it seems that trying to run the same AXMP profile with the 4 modules installed fails. It is activated without any issue via BIOS but on reboot, frequency is set back to 1866MHz which I believe is due to a safe setting on BIOS (not sure how it is called atm) in case OC fails.
At first I thought it could be an issue with the new modules so I tested them both on the correct position that MB indicates (2 and 4 as I used to have the older modules) separately. The result is that both new and old modules work fine OC'ed at 3200MHz when only 2 DIMMS are used.
With manually configuring it via BIOS I got up to 2800MHz without using the AXMP profile. After that frequency is reset to said 1866MHz so I beleive OC fails. I would not like to manually OC them as I am inexperienced. However, do you have any idea why the same AXMP profile running at 16CL and 3200Hz is not working with 4 modules installed but only with two?
Thank you for every answer, it is highly appreciated.

Recently decided to upgrade from 2x8 G.Skill Trident F4-3200C16-8GTZR to 2 more thus 4x8. I used to run the two modules with AXMP profile turned on at 3200MHz without any issue.
Some specs:
CPU: AMD Ryzen 7 2700X
MB: MSI 450 Tomahawk max
4XDIMMS: G.Skill Trident F4-3200C16-8GTZR
ISSUE: So it seems that trying to run the same AXMP profile with the 4 modules installed fails. It is activated without any issue via BIOS but on reboot, frequency is set back to 1866MHz which I believe is due to a safe setting on BIOS (not sure how it is called atm) in case OC fails.
At first I thought it could be an issue with the new modules so I tested them both on the correct position that MB indicates (2 and 4 as I used to have the older modules) separately. The result is that both new and old modules work fine OC'ed at 3200MHz when only 2 DIMMS are used.
With manually configuring it via BIOS I got up to 2800MHz without using the AXMP profile. After that frequency is reset to said 1866MHz so I beleive OC fails. I would not like to manually OC them as I am inexperienced. However, do you have any idea why the same AXMP profile running at 16CL and 3200Hz is not working with 4 modules installed but only with two?
Thank you for every answer, it is highly appreciated.