voltage fluctuation observed in two parallel Li-socl2 battery
Ohhh boy.... Please immediately stop using these primary lithium metal batteries in parallel without additional protection. You must use a diode on every cell to prevent the current from flowing into that cell - because these are non-rechargeable chemistries that have a chance of catching fire when mishandled this way. You do not want to deal with a lithium metal fire in any capacity.

When you receive the batteries, you should de-passivate them - put a 20 ohm load across the battery for upto a minute (monitor voltage). In storage these batteries become passivated and need a wake-up before being put in service.