I did not check on ios 10 but on iOS 12-13 this issue was not present and on iOS 14 it did appear. Is it an iOS bug or an expected behaviour? if it is expected how can it be fixed?
instanceofme
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i have discovered that it depends on order of hold/unhold. If you need to swap calls you need first to put one on hold(CXSetHeldCallAction isOnHold=1) and then unhold another(CXSetHeldCallAction isOnHold=0). For me it did solve the issue.
what helped to me: Right-click on any opened tab, "Close other tabs". would not say it is now ideal, but much better than it was.