The TC30 is not a CIB machine. Each time you change a tool, it gets written to the LCTLAUF. I have heard that this chip may get flaky. Also these are PC based controls. When was the last time you did a scan disk or defrag? It is possible the logic power supply filtering capacitors are leaking (electrolytic). This is an electrical term meaning they are not working as well. Possible the hard drive is misreading. Possible you have a loose connection. When was the last time you changed the air filter? The entire machine needs to work in unison.
How about spindle drift? It would make the tool change fail just when the head comes up after releasing the tool.
I have to remember what is inside a VMC with a CIB. I just worked on one too, two weeks ago. Shorted encoder. Also had to adjust the drift on the spindle drive. All the above applies but I cannot remember if the current tool is written to a chip on a board or written to the CFGPRMS.SYS file. Interesting that 2 machines have done this. Could also be heat related.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)