I'm aware of the document you have found however it doesn't tell you how the ship gets to Bremerhaven from Shanghai. It just tells you when the ship rejoins scheduled services.Glovis Symphony looks to be headed to Bremerhaven and Antwerp, but alas not Southampton.
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What it does confirm is that GLOVIS SYMPHONY is coming to Europe and will be here in early August.
At the moment I'm still hopeful the ship is chartered to Tesla. (Because it's chartered you won't find it's itinerary online)