To sum up your post in sentence, it can be said that you would like seek solution from the members of this forum because of the decline in the productivity of your employees. You have assumed that the decline in productivity is because of decline in employees' engagement.
Employee productivity depends on two factors. First one is capability. Capability is product of knowledge and skills. Therefore, first check their capability. Have you recruited misfits or they may be fit but they lack sufficient knowledge and skills. Therefore, there is limit to what they can deliver.
The second factor on which productivity depends is employee motivation. Employee engagement is little away. Before engagement comes employee motivation. Have you measured their level of motivation? Employee motivation is too complex and depends on so many factors. You may click on the hyperlink to know my previous reply on this subject. For employee engagement click on the hyperlink to refer my previous reply.
From India, Bangalore
As stated by you , there is drop in employee productivity during last two months and prior to that was is ok?
Your approach of one to one meeting and finding out the reasons for drop will certainly yield results. You may discover that they are unhappy for variety of reasons, prominently among them could be ,inadequate compensation, unchallenging work, no career growth, too much regimentation, inflexible and rigid approach and quality of supervision. Based on your feedback, you may pinpoint the reasons for drop and take corrective actions.
From India, Mumbai