Accordions don’t collapse after viewing

This is an excellent plugin. I’m using it on a client site and we’ve hit a problem.
I can open an accordion but not close it using the – toggle. If I open a second accordion, the first one closes fine. But I cannot then open the first one again. I can go down the list opening each accordion, which closes the previously open one but I am unable to open an accordion that has been closed by opening another.

I have deactivated all plugins except the Accordion plugin and the problem remains.
If I change the theme to ‘Twenty Twenty’ the problem is resolved. Unfortunately, the client uses a customised Stack theme that has had too much work done to justify replacing it.

Any ideas on how to get around this conflict? Thanks

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