Very odd error - is this a running out of memory problem?

My game is already quite large: Info returns 625/8192 tokens, 44213/65535 chars, 10994/15616 compressed. If it's relevant, the Pico-8 file itself is just a bunch of #includes of external .lua files I'm editing with VSCode.

The error I'm getting is this:

syntax error line 5 (tab 0)
::move_along::
<goto move_along> at line 5 (tab 0) jumps into the scope of local '(for compound)'

Everything was working fine an hour ago, but then I added about another 50 lines of code, including these:

if ((turns[dir.up]) and (e.dir!=dir.down)) dist[dir.up]=sqr(ex-px)+sqr(ey-1-py)

if ((turns[dir.right]) and (e.dir!=dir.left)) dist[dir.right]=sqr(abs(ex+1-px))+sqr(abs(ey-py))

if ((turns[dir.down]) and (e.dir!=dir.up)) dist[dir.down]=sqr(abs(ex-px))+sqr(abs(ey+1-py))

if ((turns[dir.left]) and (e.dir!=dir.right)) dist[dir.left]=sqr(abs(ex-1-px))+sqr(abs(ey-py))

Here's the thing: if I comment out any one of those lines, everything runs and I get no error.

I can also leave all of those four lines in, but go to a different part of the code entirely and comment out a bunch of stuff, and again, then everything runs with no error.

So you can see why I'm wondering if this is a memory problem.

Please help, I have no idea how to proceed???