Since bug 1777890 landed (which properly releases old chunk in all processes), I haven't been able to reproduce this issue. Florian, when possible could you please use your superpowers to see if you still experience this issue?
Bug 1777431 Comment 3 Edit History
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Since bug 1777890 landed (which properly releases old chunks in all processes), I haven't been able to reproduce this issue. Florian, when possible could you please use your superpowers to see if you still experience this issue?