Hello,
I added two AFF250 nodes to a cluster fas2750 existing already switched. all nodes are in ONTAP 9.9.1P1.
The new cluster 4 nodes is running fine. All cluster interconnect ports are up. the cluster ring show no errors.
All tests of "Config advisor" about the cluster are passed with succesfully. however "Config advisor" return a warning (medium impact) about the switch configuration (see bellow).

My infrastructure :
2 x BES-53248 cluster switch
!System Description "BES-53248A1, 3.4.4.6, Linux 4.4.211-28a6fe76, 2016.05.00.05"
!System Software Version "3.4.4.6"
Filename : BES-53248_RCF_v1.6-Cluster-HA.txt
Date : Oct-20-2020
Version : v1.6
Port Usage:
Ports 01 - 04: 10GbE Cluster Node Ports
Ports 55 - 56: 100GbE Cluster ISL Ports
According to the hwu netapp I can not apply another RFC than 1.6 with this firmware version (3.4.4.6) could it come that the ONTAP version is 9.9.1RC1 and I am in 9.9.1P1 I do not think but I do not see why I have this message? do you perhaps have an answer to give me ?
BES-53248_RCF_v1.6-Cluster-HA.txt / Cluster InterConnect Switch EFOS 3.4.4.6 / 9.9.1RC1, 9.8RC1, 9.7RC1, 9.6RC1
Thanks you
Vincent.