Running version “12.0.0 for Microsoft Windows (64-bit) (April 6, 2019)”, in case that matters. I fed Mathematica the command

```
Simplify(
Integrate(
e*Exp(-e*t)*F*Exp(-F *t)* Exp(-(Lambda) - b*t)*
Integrate(
Sum((b*s + (Lambda))^y/y! *
Sum(2^(-y)*Binomial(y, z)*(b*(t - s))^(x - z)/(x - z)!, {z, 0, x}),
{y, 0, Infinity}),
{s, 0, t}),
{t, 0, Infinity}),
e > 0 && F > 0 && (Lambda) > 0 && b > 0 && Element(x, Integers))
```

(line breaks added for readability, though I don’t *think* that matters). It output the warning message

Simplify::time: Time spent on a transformation exceeded -4.03955*10^12 seconds, and the transformation was aborted. Increasing the value of TimeConstraint option may improve the result of simplification.

In fact, it gave me that message three times, and then

General::stop: Further output of Simplify::time will be suppressed during this calculation.

Twelve hours after that, it gave me an answer. The warning bugs me for a couple of reasons. First, 4.03955*10^12 seconds is thousands of years. Second, I don’t know what to make of the negative number of seconds. Third, when I Googled I didn’t see any results about this. (The only results on this site that I found are all of the form “Time spent on a transformation exceeded 300 seconds”, which is rather different.)

The number -4.03955*10^12 makes me think there’s some type of overflow error going on, but I’ve got no idea other than that.