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HPE 1920 MSTP automatically change spanning tree

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HPE 1920 MSTP automatically change spanning tree


I have a setup of 3 managed switches (ABC) (HPE 1920) they are all connected with each other (unfortunaltely i'm not allowed to post image).

I've configured VLAN 1,4 which is working fine. Then I've configured the MSTP protocol for the ports used to connect the switches. One of these ports on switch C is in discarding mode which is normal to prevent a loop in the network. This makes the link between A and C is not used.

When I disconnect the link between B and C I expect the spanning tree to be adjusted so the discarding port changes to forwarding and traffic from switch C can reach the network over link A-C. But this is not working, the port stays is discarding mode.

Anyone has an idea of what can be wrong or how to enable the automatic 'failover' detection?