Trouble with REGEXP_REPLACE in MySQL 8

Question

I recently upgraded to MySQL 8 so that I can use the new Regular Expression functions (https://dev.mysql.com/doc/refman/8.0/en/regexp.html) to clean up a lot of bad addresses. However, I'm running into trouble using REGEXP_REPLACE.

I'm starting by running a SELECT query as an example (so I can see what's going on before I run an UPDATE query):

SELECT address1_raw, CONVERT(REGEXP_REPLACE (address1_raw, '^[0-9]+ ', '') 
USING UTF8) as replaced,
CONVERT(REGEXP_SUBSTR(address1_raw, '^[0-9]+ ') USING UTF8) as captured
FROM members WHERE REGEXP_LIKE (address1_raw, '^[0-9]+ ');

The results I'm looking for are like this:

address1_raw | replaced  | captured
54 Main St   | Main St   | 54
1089 High St | High St   | 1089
67 Broadway  | Broadway  | 67

Instead, I'm getting this:

address1_raw | replaced               | captured
54 Main St   | Main St                | 54
1089 High St | Main StHigh St         | 1089
67 Broadway  | Main StHigh StBroadway | 67

I'm totally stumped! Any idea what's going on here?