Please check your php variables. Our recommendation:
- PHP 5.6 (Vtiger 6.x) PHP 7.0/7.1/7.2 (Vtiger 7.x)
- max_input_vars 6000
- max_execution_time 30000
- memory_limit = 512M and higher
- post_max_size = 128M
- max_input_time = 120
You can check other parameters too: https://it-solutions4you.com/tipstricks/vtiger-system-requirements/
