***** NOT A TEACHER *****
(1) One book says this:
"There is not much difference in meaning between -ing and the to infinitive: -ing may refer to an action in progress, whereas
the to-infintive may imply 'in general':
It's difficult finding your way around in a strange city.
It's difficult to find your way around in a strange city."
Source: L.G. Alexander, Longman English Grammar (London and New York: Longman, 1988), p. 317.
(2) Another book says:
(a) The gerund is "more immediate and more vivid": I like camping in the mountains.
(b) The infinitive is more remote and more objective: I like to camp in the mountains.
Source: Marianne Celce-Murcia and Diane Larsen-Freeman, The Grammar Book (Rowley, London, and Tokyo: Newbury House Publishers, Inc., 1983), p. 436. The two authors also credit Professors Bolinger and So.
It is only my opinion that "It's a pleasure seeing you again" would be more emotional and affectionate than the "colder" "It's a
pleasure to see you again."
HAVE A NICE DAY!