Difference between ISL83078EIBZ and ADM483-EAR for UART-RS485 Converter
A few comments:

1) What is the receiver side of your design? Is the receive pin on your device 5 volt tolerant? If not, DO NOT mate with a 5 volt transceiver unless you are ok with the risk of permanent damage. There are plenty of good RS485 transceivers that can operate @ 3v3.

2) When the receiver enable (RE#), is LOW, the receiver is enabled. Respectively, when RE# is high, the receiver is disabled and the output is tri-state (aka HI-Z). For this reason, you should be applying an external pull-up resistor to +3v3 (10k is fine and the value is not critical). With this PU, the receiver pin on your UART will not see false start bits which could be the root cause of your observation.

3) In general, on RS485 networks, the START and END nodes should feature a local termination resistor of 100-120 ohms. In addition, if the transceivers are NOT fail-safe biased internally then you must consider to apply external PU and PD resistors to assist with this idle state parking. Google on the topic of fail safe resistors and there are some good notes from TI and others with calculators that take into consideration the # of nodes in your network, the transceiver impedance and the cable length.

4) A comment that is worth noting is that we are using ISL3173 on some designs and killed some hours of our life in missing the detail on the enable requirements for the transceiver. That is, when we migrated from our usual 10k PU to say enable the RS485 transmitter - the same 10k value failed to enable the Intersil ISL3173E transmitter. The datasheet specifically states that a stronger pull-up is required so a value 1k-3k is required. Be cautious of this detail.

In reviewing the Intersil / Renesas part you are using, you have the SAME restriction on note # 18, page 8 of the current datasheet.

For giggles, take the RE# pin on this transceiver and hard strap this pin to ground to keep the receiver always enabled. Does that work to see the transmitted data? That is, this RS485_Local_Echo mode in the RS485 world.

Hope this helps.