multisim intermittent digital logic problem

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Joined Apr 3, 2019

the above circuit is part of what i have done for my first year eeng digital logic final project. the circuit works by the user inputting a number on the pushbutton pad, and loading said number into the selected shift register bank (max 4 digits), and whenever the +,-,equal button is pressed it should switch banks. that circuit is at the moment only opperated by the select switch to select the banks. i have also designed a circuit so that when the "backspace" button is pressed it will shift the selected shift register bank 4 bits left, thus deleting the most recent number. this circuit might be part of the problem.

my problem is one of the hardest to debug-an intermittent one. i launch multisim and the circuit works flawlessly, and never crashes roughly 25% of the time. the other times i have to close out multisim and open it again, and this sometimes fixes it, sometimes does'nt. i have narrowed the problem down to the clock circuit, and even more specifically believe the problem to be with the two lines highlighted above. i have tried everything i could think of. when it does fail, it always does so at Tran: 0.013s mark. once it makes it past that its fine and will not crash no matter what during that specific simulation. once i rerun chances are that its failing again. the 555 timer is running at 60hz.

Here is a link to download my simulation file for any of you who have multisim (14.1 is my version):

please let me know if you see any obvious problems or know of any solutions or suggestions, or need further clarification on how the circuit specifically opperates. is this simply a problem with multisim? thanks.
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