Not an AMBOS user, but typically when this happens on the receivers it more often indicates an aging LNB or moisture in a coax connection between you and the dish.
Since you're also using a splitter of some kind to feed that signal to more than 1 receiver, it could be a culprit, or the source powering the LNB may be losing the ability to provide sufficient current needed.
All of which would come to mind before a failing receiver, IME.
Jim "Turbo" Turvaville
SBE Certified Radio Engineer
Turbo Technical Services
From: Willie Barnett <firstname.lastname@example.org>
To: CRTech <email@example.com>
Sent: Monday, February 26, 2018 10:45 AM
Subject: [CRTech] AMR-100 signal change
Just wondering if anyone else has noticed a drop in signal from your AMBOS receiver(s)? One of them here has dropped by about 1.5 dB to the mid 7's, the other is still the same as always. (Low 9's)
I swapped input connections. No changes to either unit.
The one with the lower EbNo reported a loss of signal earlier, and it's logs appear to have been reset at about that same time. Remote units, and our backup, all show steady signal and about 1/8 the BER of the unit that "glitched".
I hope it's not indicating a receiver failure! Backups of parameters have been made... just in case.