There is no chronological issue, but there is a personal interlude with Jethro's visit to Moses.
In Chapter 17, they arrive at Rephidim and make camp there ("pitched in rephidim", KJV). All the verbs here are wayiqtol, also known as "narrative past tense". There are no translation issues.
While they are pitched at Rephidim, a bunch of stuff happens, as described in Chapters 17-18:
Chapter 17: action at Rephidim
- complain about lack of water, Moses smites the rock
- Then they were attacked by the Amalekites (this tends to happen immediately after they complain). Moses goes up with Aaron and Hur, to pray for victory.
- Then Moses builds an altar to celebrate Joshua's defeat of the Amalekites
In Chapter 17, they are still at Rephidim. At some point they leave Rephidim and arrive at the mount.
Chapter 18: Jethro visits while they are at the mount.
- Then Jethro's father in law arrives with Moses wife and two kids, greets Moses when the community is encamped by the mount, hears all the news and offers a burnt offering to the Lord
Here is the WBC commentary on the mount reference in which they conclude that this does not happen after the theophany in chapter 19:
“The mountain of God” at which Moses and Israel are camped and to
which Jethro comes with Moses’ wife and sons is Sinai/Horeb, as the
use of the same phrase at 3:1; 4:27; and 24:13 makes clear. Whatever
the time of Jethro’s rendezvous, the place quite appropriately is the
mountain of the supreme revelation of Yahweh’s Presence. If indeed
this meeting took place after the theophany of chap. 19 and the
covenant-making of chap. 24 (see Form/Structure/Setting) some more
direct reference to those momentous events might be expected here. Durham, J. I. (1987). Exodus (Vol. 3, p. 243). Dallas: Word, Incorporated.
- Then Jethro suggests that Moses delegates some authority to lighten the load. Moses agrees and then Jethro departs.
Chapter 19: Theophany
Now Chapter 19 ends the interlude with Moses and his personal life, and focuses the attention back on the Israelite community, specifying exactly when Moses went up to the mount. As part of that intro, there is a parenthetical remark that by the way, they had already left Rephidim and arrived at the mount.
Ex 19.1-2 (LEB)
In the third month, when the children of Israel were gone forth out of
the land of Egypt, the same day came they into the wilderness of
Sinai. For they were departed from Rephidim, and were come to the
desert of Sinai, and had pitched in the wilderness; and there Israel
camped before the mount.
What may be tripping you up is the parenthetical remark. Here is the WBC translation, with the paranthetical remark in bold
In the third month of the exodus of the sons of Israel from the land
of Egypt, on the very day they came to the wilderness of Sinai—they
had journeyed forth from Rephidim and come to the wilderness of Sinai,
where they pitched camp: indeed, Israel had pitched camp in sight of
the mountain— Moses went up towards God.
Durham, J. I. (1987). Exodus (Vol. 3, p. 256). Dallas: Word, Incorporated.