RSTP settings between RSG2100 switch and Siprotec 4 relays

Good day,

I am not sure if I am strungling with RSTP settings between RSG2100 switch and Siprotec 4 relays. Just to give you a picture I have 5 rings of siprotec 4 relays that connect to RSG2100switch, the rings are as follows:

1. First Ring has 10 siprotec relays if you disconnect either side of the switch all relays remain visible
2. Second Ring has 18 siprotec relays if you disconnect either side of the switch all relays remain visible
3. Third Ring has 20 siprotec relays if you disconnect either side of the switch the first 18 relays remain visible and the last two cannot be pinged
4. Fourth Ring has 21 siprotec relays if you disconnect either side of the switch the first 18 relays remain visible and the last three cannot be pinged
5. Fifth Ring has 34 siprotec relays if you disconnect either side of the switch the first 18 relays remain visible and the last sixteen cannot be pinged

By default I was expecting at least 20 relays to be visible, I have no idea where does the 18 come from. I changed the RSTP settings Max Age Time from 20 to 40 and the behavior remains the same. I have also attached Netview screen short, which indicates the relays RSTP settings. On the Netview screen short what is the difference between, MaxAge-P and MaxAge-L? I have also noticed that PBDU parameter has an error on the switch, I tried ways to clear that error with no success, including reloading factory settings. I am not sure if that is the main cause of the malfunctioning. 

Please HELP

Kind regards

Ziggy Simelane

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Split from RING REDUNDANCY.