Are there any sources that HaShem still performs 'open miracles' even during the exile?
Example of a miracle during the exile
On that day R. Eliezer brought forward every imaginable argument,3 but they did not accept them. Said he to them: 'If thehalachah agrees with me, let this carob-tree prove it!' Thereupon the carob-tree was torn a hundred cubits out of its place — others affirm, four hundred cubits. 'No proof can be brought from a carob-tree,' they retorted. Again he said to them: 'If the halachah agrees with me, let the stream of water prove it!' Whereupon the stream of water flowed backwards — 'No proof can be brought from a stream of water,' they rejoined. Again he urged: 'If the halachah agrees with me, let the walls of the schoolhouse prove it,' whereupon the walls inclined to fall. But R. Joshua rebuked them, saying: 'When scholars are engaged in a halachic dispute, what have ye to interfere?' Hence they did not fall, in honour of R. Joshua, nor did they resume the upright, in honour of R. Eliezer; and they are still standing thus inclined. Again he said to them: 'If thehalachah agrees with me, let it be proved from Heaven!' Whereupon a Heavenly Voice cried out: 'Why do ye dispute with R. Eliezer, seeing that in all matters the halachah agrees with him!' But R. Joshua arose and exclaimed: 'It is not in heaven.'4 What did he mean by this? — Said R. Jeremiah: That the Torah had already been given at Mount Sinai; we pay no attention to a Heavenly Voice, because Thou hast long since written in the Torah at Mount Sinai, After the majority must one incline.5 R. Nathan met Elijah6 and asked him: What did the Holy One, Blessed be He, do in that hour? — He laughed [with joy], he replied, saying, 'My sons have defeated Me, My sons have defeated Me.'
I believe the fusing of two pieces of wood into 1 in Yechezqel (haftarah for Vayigash) occurs in Galus Bavel (the Babylonian Exile). But then, the 10 plagues and the crossing of the Red See also occurred in Exile.
Yonah's experience with the fish and his overnight growing plant were outside Israel, but not during a time of exile.
Megillah 14a discusses whether Hallel is said on miracles that occur when in exile. Does that imply that there have been revealed miracles about which to ask the question? Depends partly on what you mean by "revealed miracle" -- does the military victory of Chanukah qualify? I realize it's in Israel, but if you consider that much violation of the norm to be a hidden miracle, we see the question of miracles and Hallel need not refer to revealed ones.