What is wrong with chess.com's computer analysis?

Regarding a bit of analysis returned by chess.com's computer...in a note given after 28. ...e5? the computer gives 28. ... Bd7 as the better line. (28... Bd7 29. Bxb7 Rd8 30. Bf3 Bc6 31. Rg1 Rd3 32. Bxc6 Qxc6 33. Kh2 Qe4 34. Rd2 Rxd2 35. Qxd2 e5 36. Qd7+ Kh6 37. g4 hxg3+ 38. Rxg3 Rxg3 39. Kxg3 Qxc4 40. Qxf5 Qxc3+ 41. Kf2 Black has a decisive advantage )  I found however that after 39. Kg3 Qc4, as given by the computer, fails to 39. Qg2+ 40. Kh4 Qg5#.

This is of course a small matter but such faulty analysis is not the first I have received from the purported "-2500 strength" computer analysis.

Remember: keep those cards and letters coming.

there are better chess analysis engines out there and chess.com's computer analysis should be the last. This faulty analysis comes from chess.com server admins that want to keep a steady server. Computer analysis takes a lot of resources if done properly. And that depends on how many minutes a computer spends to analise a move. I don't think chess.com chess engine spends a lot to analyse a move to prevent server overloading