Create a basic test file, make notes as you cut it on how you secure your stock and set zero relative to it and manage all tool changes — capturing all of this in a video would be ideal — and make a video of the entire cut, then when the problem happens you can review the video to see what happened.
To check the machine mechanically. Per the machine operating checklist: Machine operating checklist , the basic points of adjustment for a machine are:
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(for belt drive machines) Pulley set screws — verify that these are in-place and secure — be sure to check all axes/pulleys (including Z on machines w/ belt-drive Z-axis, for an HDZ, check both coupler screws).
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(for the SO3/4, X- and Y-axes, and the belt-drive Z-axis on Launch and summer 2016 SO3s) V wheels / eccentric nuts (per assembly instructions)
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(for the Pro, Pro 5, HDM, and Z-Plus and HDZ Z-axis) Lubrication of the linear rails: CNC Machine Maintenance c.f., https://web.archive.org/web/20211127125707/https://docs.carbide3d.com/assembly/linear-guide-maintenance/Linear_Rail_and_Guide_Maintenance_02-17-2021_v1.0.pdf
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(for HDZs, and HDMs, and SO5 Pros) check that couplers between the motor and ball screw are secure, for the SO5 check that the DAC which transfers the rotary motion of the ball screw to linear machine motion is secure on the carriage/gantry
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(for belt drive machines) Belt tension (see the relevant step in your instruction manual, Note that the X-axis motor is held in place on standoffs and if those bolts are loose this can cause belt tension issues. Also, belt tension for the Y-axis stepper motors needs to be even/equivalent on each side — a significant difference can cause skipping on one side eventually resulting in lost steps on both. Measuring belt tension, squaring and calibration
Naturally, this assumes that all the wiring is in good condition and all connectors secure per the Machine Operating Checklist. Verify that all wiring is in good condition and all connectors are secure, and that all wiring leading into connectors are properly in place and are secured so that the wiring leading into and away from connectors will not shift.