I upgraded to a new (to me) Apple TV box
Which model exactly?
Identify your Apple TV model - Apple Support
Find your Apple TV model number - Apple Support
… it looses signal to the (Samsung) tv.
For a second, a few seconds, or indefinitely?
Depending on the capabilities of the TV, it may take some time for a TV to adjust to changes in frame rate or changes in dynamic range over HDMI. This is as expected for TVs that do not support QMS (an optional HDMI 2.1 feature). One way to avoid this, is to set Apple TV to use a constant frame rate and a constant dynamic range (i.e. disable Match Content in the video settings). Could that be it?
Else try a different (better) HDMI cable. For devices with HDMI 2.0, an 18 Gbps rated HDMI cable is recommended. For devices with HDMI 2.1, an 48 Gbps rated HDMI cable is recommended. For HDMI 2.0 devices, YCbCr colorspace with 4:2:0 chroma setting is recommended. Could that be it?