That remark is subjective. I have had a few diesels that still prefer a few seconds glow when even warm to fire off. Otherwise they seem fine. Never knew the reason either. In your case it is easy and fairly quick to check how much glow function you have. Should do it as might lead to a truer cause like air in fuel or whatever once they are eliminated. Not wise to speculate until you are positive the glow circuit is fully functional anyways.