after press “send” Button, loading long time

Hey, I use Contact Form 7 and everything was always ok so far.
But now I found out that when you press “send” there comes the load circle and it doesn´t vanish for a long time. Clients already told me that they are not sure if I get the message, so they try it several times.
Is this a known problem? Can anybody help me?
Thank you
Samira

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