The internal server error may be caused by permission error, configurations, malicious traffic that exhaust resources allocated to user and have a shortage of memory on a site or cron job that run on the site and execute time to time or database activities. Or several other reasons, these are common.
Permission can be solved by checking and changing the permission to a correct permission. Note that a wrong permission could compromised security on a site. Be caution to avoid 777 permission.
Malicious traffic can be solved differently depending on users understanding, you can trace malicious activities ips and black-list on firewall to block access to malicious users. You can also integrate a reCAPTCHA on the login and posting pages to minimize malicious activities and several other ways.
Setting a cron job to perform some activities on the site that may require memory excessive usage can be avoided or minimize to avoid such error. And that is the case with database operation, especially synchronizing remotely require memory and may reflect the error on the site at a peak of shortage. Upgrade to a higher package is an alternative for any operation that is requiring high resources.
You can submit a ticket on any issue you cannot handle to our support department for help.