INCONSISTENT errors

[MoHabib88]

I'm not a programmer, so can someone explain to me what the HELL is going on here: why the hell does this program pop up errors, only to have them disappear by re-executing it. It makes modifying the code a real pain, because you don't know if it is you, or if the script is shitting the bed.

Example 1
Error: Unable to find class #fj, which is the find jobs button on indeed.com
Re-executed code, error went away, later came back. Seriously?

Example 2: error comes up when you run a search. no jobs get posted.
Error: block passed to #window_opened _by opened 0 windows instead of 1 (Capybara::Window Error)
Re-execute code, error went away, later comes back...

To clarify on example 2:
That error sometimes comes up since I have a Canadian IP address and it redirects me to indeed.ca. However, when used a US ip address via a VPN, that error was consistent 100% of the time. In an attempt to work around this, i've modified the code to go to the US version of the site, again, that error is consistent 100% of the time.