The problem seems to be that Flybe quote a Minimum Connection Time (MCT) of 90 minutes at SEN (the same as for STN and LHR although LCY is only 45 minutes) so the evening connections to DUB and MAN don't work.
That MCT certainly seems excessively long for SEN and perhaps they should look at that. MCT at MAN is only 60 minutes for domestic/international transfers and that would seem more reasonable.