This is a 555 timer circuit which is supposed to generate two short pulses, back to back, at a regular frequency. The top 555 is configured as astable to control the frequency. It feeds the first 555 to trigger the first pulse which in turn feeds the second to trigger the second pulse.
The middle timer behaves as expected (green it output, blue is threshold, both from middle.
However the output on the bottom timer never goes low when it triggers the threshold voltage (green is output, blue is threshold on bottom timer)
Am I missing something, or is this a limitation of LTSpice?