Check your spelling for the Family name. Did you enter ISSAC(S) instead of ISAAC(S)?
Check the century: Did you enter 1908 or 1708 instead of 1808?
A good proportion of these early records do not include English family names, have you exhausted all the Hebrew name options?
Apart from the Burial Records (DPL), all records from the registers listed on the Sources have been included in the database so, if you still haven’t found your ancestor, it may be that the event took place outside of London or, even, outside the UK, or was recorded by some organisation not yet covered by this database.