Thanks for your suggestions. The log files of my application just stop when the fetchall_arrayref call is made. I'll look into how to find the DBI and dbms logs.

What does work? Perhaps a matrix will be more clear:

Machine #1 ( used for initial testing )
                           |-----------------------------|------------
+---------------|------------------------------|
                           | no placeholders no results  | placeholder
+s with results | placeholders with no results |
                           |-----------------------------|------------
+---------------|------------------------------|
not specifying a TDS level | empty array                 | array of re
+sult hashes    | empty array                  |
                           |-----------------------------|------------
+---------------|------------------------------|
specifying a TDS level     | empty array                 | array of re
+sult hashes    | (application hangs)          |
                           |-----------------------------|------------
+---------------|------------------------------|

Machine #2 ( used for "Steps to reproduce on Ubuntu 20.04" in original
+ post )
                           |-----------------------------|------------
+---------------|------------------------------|
                           | no placeholders no results  | placeholder
+s with results | placeholders with no results |
                           |-----------------------------|------------
+---------------|------------------------------|
not specifying a TDS level | (connection fails)          | (connection
+ fails)        | (connection fails)           |
                           |-----------------------------|------------
+---------------|------------------------------|
specifying a TDS level     | empty array                 | array of re
+sult hashes    | (application hangs)          |
                           |-----------------------------|------------
+---------------|------------------------------|
[download]

For some reason the test program in my original post doesn't connect at all on machine #2 when no TDS level is specified. This is the error message, but I believe this is not related to my problem. (Or perhaps to state it more accurately, it's not the problem I'm trying to solve)

DBI connect('server=172.28.79.294','machinename',...) failed: OpenClie
+nt message: LAYER = (0) ORIGIN = (0) SEVERITY = (78) NUMBER = (49)
Server 172.28.79.294, database 
Message String: Unexpected EOF from the server
OpenClient message: LAYER = (0) ORIGIN = (0) SEVERITY = (78) NUMBER = 
+(34)
Server 172.28.79.294, database 
Message String: Adaptive Server connection failed
OpenClient message: LAYER = (0) ORIGIN = (0) SEVERITY = (78) NUMBER = 
+(34)
Server 172.28.79.294, database 
Message String: Adaptive Server connection failed
 at go.pl line 14.
Died at go.pl line 14.
[download]

My original code that produced this error had SQL queries included tables. My test code for reproducing the problem wouldn't produce the same results if you didn't have the same tables with the same columns, so I simplified them for testing.