I have pledged 51 units of LIQUIDBEES a couple of weeks ago. Now in the pledges holdings, I see 51(1) in the quantity column. What does this 1 within brackets mean? Is this the unit credited from dividends? I don’t see the dividends being credited in my CDSL account.

The number within brackets indicate the number of shares for which there is no buy average (discrepant quantities) due to various reasons such as IPO, corporate action, transfer in, etc. The current system shows such units in brackets even if it is sold.
In your case, you must have received the liquidbees dividend units sometime back and have sold it without feeding in the buy average. Hence, this unit must still be showing as discrepant. We are currently running a recalculation for such units and must be fixed in a day or two.