This can be due to the lack of extended properties in the certificate you are using on splashtop.
1. Follow the article to export the certificate with extended properties [Avalanche 6.2] Third Party Certs Missing Private Key Not Allowing Devices to Enroll
2. Once Exported upload the certificate to the splashtop center like below
3. On the device clear the application data for the Splashtop application
4. Once you clear the data start the splashtop application and check and it should look like below.