Ok, I've found and fixed the bug. It was a very silly and simple bug 
The bug basically truncated the timeout to 1 ms when using the screenshot command which made retrieval of the instrument ID fail in your case.
The fix should be available via the edge channel now. Let me know if it works for you. Thanks.
lxi screenshot -a scope -p rs-hmo1000
works.
> lxi screenshot -a scope
Loaded rs-hmo1000 screenshot plugin
hangs.
no change when using IP. still hangs.
with gdb, I get (but probably not much good to you).
#0 0x00007ffff76b76f0 in __poll_nocancel () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007ffff76f14e3 in readtcp (ctptr=0x60a6b0 "\004",
buf=0x60e3d0 "d, Robert Gauthier, Floyd Wilder, Mark Drissel, Kenny Lyons,\n# Paul Dunne, Tirath Pannu, Mike L", len=4000) at clnt_tcp.c:480
#2 0x00007ffff76ea946 in fill_input_buf (rstrm=0x60a770) at xdr_rec.c:567
#3 get_input_bytes (len=4, addr=0x7fffffbecbac "", rstrm=<optimized out>) at xdr_rec.c:586
#4 set_input_fragment (rstrm=<optimized out>) at xdr_rec.c:605
#5 xdrrec_getbytes (xdrs=<optimized out>, addr=addr@entry=0x7fffffbecbfc "\377\177", len=len@entry=4)
at xdr_rec.c:262
#6 0x00007ffff76eab83 in xdrrec_getlong (xdrs=<optimized out>, lp=0x7fffffbecc18) at xdr_rec.c:218
#7 0x00007ffff76f6aab in __GI_xdr_u_long (xdrs=xdrs@entry=0x60a718, ulp=ulp@entry=0x7fffffbecca0) at xdr.c:214
#8 0x00007ffff76e9791 in __GI_xdr_replymsg (xdrs=xdrs@entry=0x60a718, rmsg=rmsg@entry=0x7fffffbecca0)
at rpc_prot.c:135
#9 0x00007ffff76f12ae in clnttcp_call (h=0x60a690, proc=10, xdr_args=0x7ffff7bd07f1 <xdr_Create_LinkParms>,
args_ptr=0x7fffffbecdb0 "\220\246`", xdr_results=0x7ffff7bd0ad1 <xdr_Create_LinkResp>,
results_ptr=0x60a0e8 "\210\v\230\367\377\177", timeout=...) at clnt_tcp.c:287
#10 0x00007ffff7bd01e8 in create_link_1 () from liblxi.so.1
#11 0x00007ffff7bcedb2 in vxi11_connect () from liblxi.so.1
#12 0x00007ffff7bcea0e in lxi_connect () from liblxi.so.1
#13 0x0000000000404339 in rs_hmo1000_screenshot ()
#14 0x0000000000403525 in screenshot ()
#15 0x0000000000402384 in main ()