More information needed.
Is just one particular drive causing the crash? One particular dock?
Or a change from X number of drives being data destructed to X+1 drives being data destructed and the quantity increase causes the crash?
What is the hardware environment: host computer/system for the 25 external docks?
What OS system in the host computer using? Windows 10?
Does KillDisk provide any progress or error reporting regarding data destruction and results?
Windows 10 - Look in Reliability History for entries related to the crashes.
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As just a opening thought I would suspect that the PSU cannot (no longer) meet the power demands of all of the drives undergoing data destruction plus the power demands of the host system OS and/or resources needed to sucessfully run "KillDisk".
PSU has begun to fail and falter and when some threshold power demand is hit then a crash occurs.
Update your post to include full system hardware specs and OS information.
Include PSU: make, model, wattage, age, condition.