This seems to be an ugly issue.I would recommend to check:
- Correct earthing of your SV04 (power supply unit, mainboard and metal case and gantry parts);
- power supply output voltage and mainboard supply voltage during the auto levelling procedure - both voltages have to remain stable;
- CR touch & connected cables - there must be no electrical interruption when manually wiggling the cables;
- left print head cable connectors & left gantry breakboard for brittle solder joints;
- the surrounding environment of your SV04 - are the any new electrical devices that might cause electromagnetical interference? Extra distance could help, shielded cables will help.
Good luck!
Björn