I suggest you remove Office Online server farm from SharePoint and recreate the Office Online server farm from SharePoint.
To remove Office Online server farm from SharePoint and recreate the Office Online server farm from SharePoint, refer to the following steps.
Take farm offline (if there is a load balancer)
Collect the current Farm information via Powershell (on WAC Server):
Import-Module -Name OfficeWebApps
Get-OfficeWebAppsFarm > c:\MyWACfarm.txt
(If multi-server farm) use Powershell (on WAC Servers) to remove each child machine from the farm, then remove the parent machine. This will delete the farm.
Reboot the Office Web Apps server(s).
5.Recreate the farm via Powershell (on WAC Server) using (if appropriate) the parameter values from "MyWACfarm.txt".
New-OfficeWebAppsFarm -InternalURL "http://WACServer.corp.contoso.com" -AllowHttp -EditingEnabled -OpenFromURLEnabled
Note: You may want to rebuild the bindings via SharePoint Powershell (on SharePoint Server):
New-SPWOPIBinding -ServerName "WACServer.corp.contoso.com" -AllowHttp
Note: Anything above in you need to replace with the correct information from your farm.