The red light was a LOS (loss of signal) indication and a green flashing PON light is an indication that there is a signal but your ONT hasn’t been recognised at the ‘headend’ equipment, where previously it had (because it worked for a time ) .
This is effectively two different problems, in basic terms you had no ‘light’ coming into your ONT , and that’s been replaced by having ‘light’ but from the wrong place …a scenario that could provide a set of circumstances that would account for that , is a cable fault between the headend and splitter node (so for arguments sake someone cuts an optical cable containing many ‘connections’ ) , when reconnecting /repairing the damaged cable someone makes an error , so instead connecting fibre A to A , B to B , C to C etc, they connect A to B , B to C , and C to A , obviously I’m not saying that is the issue here (and my example is over simplified to hopefully aid understanding) but something like that could explain someone experiencing 2 errors in succession…there are other possibilities, like your ONT has developed a fault and has stopped communicating with the headend , but I’m not trying to identify your specific problem, just indicating the type of thing that can happen in the network.
Its not likely to be an account issue with BT , that is more likely to show up as you having a solid green PON light on the ONT , and an error light on your router , but it’s unimportant anyway , even if the error is on the Openreach network you need to contact BT who in turn need to advise Openreach .
There is a pretty reasonable chance that if it’s Openreach’s problem affecting many customers , they already know about it ,(perhaps ask near neighbours on Openreach FTTP if they are having issues ) but you still should report it to BT , that way should the delay in repair take some time, at least your fault is recorded with BT so any compensation can be calculated
