Was my solution no good?  It seemed to work with the data you provided...

A sample solution (not an efficient or "good" one but it works with the sample data you gave, but no promises it would work with "real" data, and I imagine...

There are a lot of good articles written pertaining to SSRS and timeouts out there, such as this one:
http://geekswithblogs.net/ssrs/archive/2009/10/30/steps-to-resolve-ssrs-timeout-issues.aspx

There are 2 basic approaches to timeout issues...

I generally tell them that "I am a database administrator; which is a spcific role in the IT industry."  It gives them the chance to ask more questions about it...

I am probably the "odd duck" in the group, but I don't find any software is "just a toaster".
For years, I just used notepad because it was pre-installed and...

My methodology is that NULLs are acceptable if you can justify them.  If I see code where a developer is creating a table and they haven't talked to me first...

Is this a live server?
If so, my first step would be to get a TEST server set up so you can do changes during company uptime and not have...

Pretty sure the only good way to do that is to cast it to a numeric type in the report or casting it as something else inside excel.  
But...

Anything in the SQL Server Agent Error Log?  That should tell you why it failed to start.

There are a lot of things you can check:
While the process is running, look at the CPU's (and other resoureces) in resource monitor.  How many cores are being fully...

I think what you would want is something like in this webpage:
https://jwcooney.com/2015/03/02/ssrs-simple-code-examples-of-handling-null-or-blank-date-fields/
or this page:
https://www.experts-exchange.com/questions/20862294/cint-error-when-field-is-null.html

basically, you want to check if the value is blank...

Could you post your restore script?

I have personally not experienced this, but I am wondering if maybe something in your restore script it touching DB B.

Update - so I tried everything in the SSRS configuration that I could find to change the user and every time it is the same thing.  Works great with every...

What I used to do in situations like that is instead of getting a static IP from my ISP (which cost extra money) is to use a free DNS service...