Let's imagine the following situation:
We have a party of adventurers: Tom the Wizard, Bob the Cleric and Jerry the Monk. The three adventurers are surrounded by many ill-intended creatures.
Tom casts an 8th-level globe of invulnerability (surrounding himself and his friends -- let's say he does not get counterspelled), then Bob the Cleric triggers a Stunning symbol (for example, by saying "Activate!") on the ground next to the limit of the globe (that Bob had previously inscribed there). The enemies fail their save and are now stunned, but the three adventurers, being inside the globe, aren't affected. Jerry now wants to go outside the globe, whack an enemy or two, then go back inside the globe to end his turn inside of it.
The symbol spell, as well as other lingering areas of effect, says that "any creature that enters the sphere or ends its turn there is affected".
When Jerry leaves the globe, is he considered as having entered the symbol's sphere (thus needing to make the saving throw), or was he already considered to be inside of it, even if the globe protected him from its effects (thus not having to make the saving throw when he leaves the globe)?
My hesitation relies on the fact that, here, Jerry is within the sphere created by the symbol, but the globe's text says that "The barrier also blocks areas of effect that reach its area". Not sure here if the word "blocks" makes it so that you're still considered inside the area or not.
The question also applies for other lingering spells that affect creatures when they enter the area.