Are you by chance progressing in the research tree and activating squad size upgrades? If so, your actual number of troops is not decreasing, but the number of squads does decrease when there are more troops per squad. You should be able to hover over a particular unit in the Army Camp tab and see the number of troops/troops per squad/number of squads. Units are weighted; this means some units have less troops per squad than others. And your squad size will display in the upper right corner as well. Building and upgrading armories will increase the number of units you can train at a time, so try to keep up with those upgrades to improve your rate of production as you get bigger and bigger squads. At some point right before or at the beginning of guest races you'll need to evaluate the pros/cons of continuing to take all available squad size upgrades or declining the optional ones. Larger squad sizes are beneficial for clearing provinces on the world map, but tend to make tournament provinces more expensive. Early on, you need to build up a reasonable squad size, just be aware that may not continue to be true later on.