go to Dashboard > Tools > Site Health and first make sure there are no errors being reported.
Then check the Info > Server setup to make sure you have enough server resources. These are my default settings:
PHP max input variables 4000
PHP time limit 1200
PHP memory limit 256M
Max input time 600
Upload max filesize 300M
PHP post max size 1000M
Some of your values are extremely low.
Check with your host, and ask them if the can set debug mode and check the error_log to see whats happening when the customizer is not working. They may be able to advise.