Yes, I do have a X-T30. At this moment, I have a Sandisk Extreme Pro 170MB, 64 gb card in it that works just fine for what little video I record using that camera. But I have a selection of other cards that save video files also just fine, including Transcend and Lexar. But they are all rated as being fast enough for 4k recording, the slower cards made by those same companies can only record 640 or 1080p not 4k. The rating matters.
Which sd card are you using?
The ones listed on this site are decent:
but as long as your card meets the minimum requirements, it should be okay. Did you try using a different card?