Question about EST2's SDC topology and addressing

[S1ider]

Good evening Everyone,

I ask help of honorable community, problem is follow - we have building it has installed old Mirtone FACP (actually it's EST2). This panel has permanent trouble condition (of course it is "0016 - Loop 1 Device Mapping Error"). This panel has been installed more 20 years ago, company-installer no more exist, CHUBB has advise us to upgrade system, we don't have Lvl3 password (I don't see necessity bruteforce it), we don't have 2-SDU and of course don't have config-files of this system. Anyway, we will plan to upgrade this panel in the near future. It will be not a panel by Edwards, I suppose it will be Mircom FX-2000 or FX-4000. I am in process of preparation information for upgrade system, and now I am on stage drawing/understanding of existing SIGA-circuit. I am don't have enough experience of working with SIGA-circuits and I can't understand next (it seems to me logically unexplained even considering on T-taps) - for example, we have the some module (let it be the GSA-CT1) with address 0220 on our SIGA-circuit. When we disconnect wire from module's connector #1 (it's 'Data Out -') then panel has lost some devices on this branch placed after this module (for example, devices with addresses 0221, 0222, 0223, 0224). It is expected. When we disconnect wire from module's connector #4 (it's 'Data In +') then to this list of lost devices adds not only this device (it will be logically) but some additional devices, that is to say the panel lost devices with addresses 0220, 0221, 0222, 0223, 0224, 0260, 0262, 0270, 0280, for example. This is not a glitch, this result is repeatable. Can anybody explain to me how is it possible?