Day Trader’s Weekend Aftermarket Lounge 1-3 Feb 2019, page-34

not so sure you should be too hard on yourself here ......... without knowing all the circumstances (i do not want to know any more) i have no idea but CHESS (asx managed) is the actual place where the "ownership" of the shares is recorded and who the sponsored broker is (via PID) - and chess knows what shares are subject to DvP on a daily basis - ie Delivery vs Payment T+2.

what i mean is the shares cannot just show up at your new broker until chess/old broker has done the transfer paperwork for the HIN/PID change.
The gaining broker is the one that initiates the xfer paperwork, and sends it to the losing broker. the losing broker would be dumb not to remove your access to the holdings as they process "match" the xfer forms. this is the bit that screams at me now for ur issue.

i xfer shares a lot - and have sometimes sold parcels days later after i have sent xfer forms (but before actual xfer)  - and never had a problem like u say.
some of my losing brokers send me a contract note when these transfers occur - a sell for nil consideration - something to do with their bookkeeping i spose.  but most do not - the shares just disappear from old and the later appear at the new broker (same day/next day) and the new chess form in the mail next month for hin quantity changes. The register is also involved in this recording process as well (link, boardroom etc).

brokers do this every day of the week - they have systems - something has gone wrong i reckon (with their system) .........

good luck