In fact, it could be anything. Perhaps this is some kind of malware that somehow prevented the sending of your bitcoins. Therefore, you should always carefully check the wallet address and the authenticity of the site you are visiting.
most likely indeed that is what happens because now there are so many malware viruses circulating in phishing sites, which allows not only coins to be lost but all important data will be easily retrieved.
We recommend that you double-check the computer that is used to transfer the coin, it is possible that the malware has attacked the system.