There are two aspects here.
1. You blithely turn left into Meadvale road and park for several days running, not noticing the restriction signs, then whallop, you get a PCN, then several more in the post. The first PCN arrival alerts you to the restriction.
In cases like this, it is generally best when submitting reps to the council to state that you only became aware of the restriction when the first PCN dated <date> arrived in the post on <date>, but in between these dates four more PCNs were posted but only arrived after you received the first one and was alerted to the restriction. You should say that you consider having to pay 5 PCNs is a grossly excessive penalty especially as you only became aware of the restriction 8 days later when the first PCN arrived. Ask that PCNs 2-5 be cancelled.
2. The obscured signage
This restriction has been in place since 2021, so I am a bit surprised you know nothing about it.
This winter GSV view shows the restriction signs, as there are no leaves on the tree, plus a rather misleading "new road layout" sign which is meaningless, it should have been a warning about the left turn.
https://maps.app.goo.gl/MMghQJgFGaeZQTXr6Later in 2021, the signs are totally obscured by the tree foliage
https://maps.app.goo.gl/hobETQszfz6unz9f8and
https://maps.app.goo.gl/JpCF2N3HCBRrGFRV9I would say you have a pretty powerful case on sign obscuration. In fact, if one studies the signs of 2021, originally the restriction sign was placed behind the tree ! the later view shows it was moved forward, sometime between January and June 2021.