Just based on keywords, it might be Rebecca Ore's "Hypocaust & Bathysphere" as per this review of Lightspeed Magazine, May 2017 (a reprint of its 1995 release in Asimov's Science Fiction, January 1995):
The novella reprint "Hypocaust & Bathysphere" had a very interesting premise: Time travelers show up in 1348 in Britain to study the origins of the plague. The locals, weirdly, are very accustomed to time travelers. They know about paradoxes and are concerned they will all die of the plague in order to avoid temporal difficulties, as they all know about the future.
Line that made me snigger? "If those time people are so concerned about paradoxes, they shouldn't sneak in canned drinks." (The Lord of the manor likes Coke products.)
Unfortunately, after that great start, things just got weird for me, especially the rape-y bits. The local Lord makes a habit of sleeping with time traveling women, and the current woman (Sara) oddly acquiesces to having sex with him on their second meeting, even though it's a dumb idea, and then gets passed off to the local priest's younger brother who wants to get her pregnant, and it IS rape and... I have no interest in reading about this sort of thing, especially as the rest of the story ended up just as dismally.
An excerpt discussing how previous travelers were found out by their clothing:
The Lord wondered why God always sent him such obvious peasants.
Cleaner than their ancestors, though. He wondered if time travelers
realized that the very threads of their clothes made people nervous. His
wife, after much examination of time traveler clothes, said that the
machines that made time travelers’ clothes were too dumb to leave subtle
messages in the spinning and weaving. That’s why the villeins had
turned their wool combs on the first time traveler. He wore inhuman
clothes and was obviously no saint. He also perhaps discovered a pot
quern or two, or a fulling trough. Some villeins couldn’t be broken of
cheating their Lord’s mills.
The second time traveler looked like a peasant trying to evade her
Lord’s fulling mill by weaving and wearing unfulled cloth so sleazy one
could see through the loose weave. Underneath, she wore brain-dead
machine cloth. The Lord knew none of them expected to be undressed
by fourteenth century hands. From her, the Lord had learned how to
unhook bras.
When they caught up to his horse the third time, the Lord said, “At
least, you didn’t try to fool us with bad post-Modern hand spinning and
weaving.”
I believe I found it via search terms of hypocaust "time traveller" albeit not on the first page. It was not the story I remembered (which I think actually may have been Andre Norton's The Time Traders).
